Merge branch 'es/wt-add-detach'

"git worktree add" learns that the "-d" is a synonym to "--detach"
option to create a new worktree without being on a branch.

* es/wt-add-detach:
  git-worktree.txt: discuss branch-based vs. throwaway worktrees
  worktree: teach `add` to recognize -d as shorthand for --detach
  git-checkout.txt: document -d short option for --detach

Documentation/git-checkout.txt

@@ -198,6 +198,7 @@ Use `--no-guess` to disable this.
 	Create the new branch's reflog; see linkgit:git-branch[1] for
 	details.
 
+-d::
 --detach::
 	Rather than checking out a branch to work on it, check out a
 	commit for inspection and discardable experiments.

Documentation/git-worktree.txt

@@ -32,6 +32,18 @@ A repository has one main working tree (if it's not a
 bare repository) and zero or more linked working trees. When you are done
 with a linked working tree, remove it with `git worktree remove`.
 
+In its simplest form, `git worktree add <path>` automatically creates a
+new branch whose name is the final component of `<path>`, which is
+convenient if you plan to work on a new topic. For instance, `git
+worktree add ../hotfix` creates new branch `hotfix` and checks it out at
+path `../hotfix`. To instead work on an existing branch in a new working
+tree, use `git worktree add <path> <branch>`. On the other hand, if you
+just plan to make some experimental changes or do testing without
+disturbing existing development, it is often convenient to create a
+'throwaway' working tree not associated with any branch. For instance,
+`git worktree add -d <path>` creates a new working tree with a detached
+`HEAD` at the same commit as the current branch.
+
 If a working tree is deleted without using `git worktree remove`, then
 its associated administrative files, which reside in the repository
 (see "DETAILS" below), will eventually be removed automatically (see
@@ -164,6 +176,7 @@ To remove a locked working tree, specify `--force` twice.
 	exists. `-B` overrides this safeguard, resetting `<new-branch>` to
 	`<commit-ish>`.
 
+-d::
 --detach::
 	With `add`, detach `HEAD` in the new working tree. See "DETACHED HEAD"
 	in linkgit:git-checkout[1].

builtin/worktree.c

@@ -555,7 +555,7 @@ static int add(int ac, const char **av, const char *prefix)
 			   N_("create a new branch")),
 		OPT_STRING('B', NULL, &new_branch_force, N_("branch"),
 			   N_("create or reset a branch")),
-		OPT_BOOL(0, "detach", &opts.detach, N_("detach HEAD at named commit")),
+		OPT_BOOL('d', "detach", &opts.detach, N_("detach HEAD at named commit")),
 		OPT_BOOL(0, "checkout", &opts.checkout, N_("populate the new working tree")),
 		OPT_BOOL(0, "lock", &opts.keep_locked, N_("keep the new working tree locked")),
 		OPT__QUIET(&opts.quiet, N_("suppress progress reporting")),