rev-list-options.txt: start a list for show-pulls

The explanation of the `--show-pulls` option added in commit 8d049e182e
("revision: --show-pulls adds helpful merges", 2020-04-10) consists of
several paragraphs and we use "+" throughout to tie them together in one
long chain of list continuations. Only thing is, we're not in any kind
of list, so these pluses end up being rendered literally.

The preceding few paragraphs describe `--ancestry-path` and there we
*do* have a list, since we've started one with `--ancestry-path::`. In
fact, we have several such lists for all the various history-simplifying
options we're discussing earlier in this file.

Thus, we're missing a list both from a consistency point of view and
from a practical rendering standpoint.

Let's start a list for `--show-pulls` where we start actually discussing
the option, and keep the paragraphs preceding it out of that list. That
is, drop all those pluses before the new list we're adding here.

Helped-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -581,12 +581,12 @@ option does. Applied to the 'D..M' range, it results in:
 
 Before discussing another option, `--show-pulls`, we need to
 create a new example history.
-+
+
 A common problem users face when looking at simplified history is that a
 commit they know changed a file somehow does not appear in the file's
 simplified history. Let's demonstrate a new example and show how options
 such as `--full-history` and `--simplify-merges` works in that case:
-+
+
 -----------------------------------------------------------------------
 	  .-A---M-----C--N---O---P
 	 /     / \  \  \/   /   /
@@ -595,7 +595,7 @@ such as `--full-history` and `--simplify-merges` works in that case:
 	  \ /      /\        /
 	   `---X--'  `---Y--'
 -----------------------------------------------------------------------
-+
+
 For this example, suppose `I` created `file.txt` which was modified by
 `A`, `B`, and `X` in different ways. The single-parent commits `C`, `Z`,
 and `Y` do not change `file.txt`. The merge commit `M` was created by
@@ -607,19 +607,19 @@ the contents of `file.txt` at `X`. Hence, `R` is TREESAME to `X` but not
 contents of `file.txt` at `R`, so `N` is TREESAME to `R` but not `C`.
 The merge commits `O` and `P` are TREESAME to their first parents, but
 not to their second parents, `Z` and `Y` respectively.
-+
+
 When using the default mode, `N` and `R` both have a TREESAME parent, so
 those edges are walked and the others are ignored. The resulting history
 graph is:
-+
+
 -----------------------------------------------------------------------
 	I---X
 -----------------------------------------------------------------------
-+
+
 When using `--full-history`, Git walks every edge. This will discover
 the commits `A` and `B` and the merge `M`, but also will reveal the
 merge commits `O` and `P`. With parent rewriting, the resulting graph is:
-+
+
 -----------------------------------------------------------------------
 	  .-A---M--------N---O---P
 	 /     / \  \  \/   /   /
@@ -628,21 +628,21 @@ merge commits `O` and `P`. With parent rewriting, the resulting graph is:
 	  \ /      /\        /
 	   `---X--'  `------'
 -----------------------------------------------------------------------
-+
+
 Here, the merge commits `O` and `P` contribute extra noise, as they did
 not actually contribute a change to `file.txt`. They only merged a topic
 that was based on an older version of `file.txt`. This is a common
 issue in repositories using a workflow where many contributors work in
 parallel and merge their topic branches along a single trunk: manu
 unrelated merges appear in the `--full-history` results.
-+
+
 When using the `--simplify-merges` option, the commits `O` and `P`
 disappear from the results. This is because the rewritten second parents
 of `O` and `P` are reachable from their first parents. Those edges are
 removed and then the commits look like single-parent commits that are
 TREESAME to their parent. This also happens to the commit `N`, resulting
 in a history view as follows:
-+
+
 -----------------------------------------------------------------------
 	  .-A---M--.
 	 /     /    \
@@ -651,18 +651,18 @@ in a history view as follows:
 	  \ /      /
 	   `---X--'
 -----------------------------------------------------------------------
-+
+
 In this view, we see all of the important single-parent changes from
 `A`, `B`, and `X`. We also see the carefully-resolved merge `M` and the
 not-so-carefully-resolved merge `R`. This is usually enough information
 to determine why the commits `A` and `B` "disappeared" from history in
 the default view. However, there are a few issues with this approach.
-+
+
 The first issue is performance. Unlike any previous option, the
 `--simplify-merges` option requires walking the entire commit history
 before returning a single result. This can make the option difficult to
 use for very large repositories.
-+
+
 The second issue is one of auditing. When many contributors are working
 on the same repository, it is important which merge commits introduced
 a change into an important branch. The problematic merge `R` above is
@@ -671,10 +671,13 @@ important branch. Instead, the merge `N` was used to merge `R` and `X`
 into the important branch. This commit may have information about why
 the change `X` came to override the changes from `A` and `B` in its
 commit message.
+
+--show-pulls::
+	In addition to the commits shown in the default history, show
+	each merge commit that is not TREESAME to its first parent but
+	is TREESAME to a later parent.
 +
-The `--show-pulls` option helps with both of these issues by adding more
-merge commits to the history results. If a merge is not TREESAME to its
-first parent but is TREESAME to a later parent, then that merge is
+When a merge commit is included by `--show-pulls`, the merge is
 treated as if it "pulled" the change from another branch. When using
 `--show-pulls` on this example (and no other options) the resulting
 graph is: