docs: add and use include template for config/* includes

In b6a8d09f6d (gc docs: include the "gc.*" section from "config" in
"gc", 2019-04-07) the "git gc" documentation was made to include the
config/gc.txt in its "CONFIGURATION" section. We do that in several
other places, but "git gc" was the only one with a blurb above the
include to orient the reader.

We don't want readers to carefully scrutinize "git-config(1)" and
"git-gc(1)" looking for discrepancies, instead we should tell them
that the latter includes a part of the former.

This change formalizes that wording in two new templates to be
included, one for the "git gc" case where the entire section is
included from "git-config(1)", and another for when the inclusion of
"git-config(1)" follows discussion unique to that documentation. In
order to use that re-arrange the order of those being discussed in the
"git-merge(1)" documentation.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/Makefile

@@ -51,6 +51,7 @@ HOWTO_TXT += $(wildcard howto/*.txt)
 
 DOC_DEP_TXT += $(wildcard *.txt)
 DOC_DEP_TXT += $(wildcard config/*.txt)
+DOC_DEP_TXT += $(wildcard includes/*.txt)
 
 ifdef MAN_FILTER
 MAN_TXT = $(filter $(MAN_FILTER),$(MAN1_TXT) $(MAN5_TXT) $(MAN7_TXT))

Documentation/git-fsck.txt

@@ -107,6 +107,8 @@ care about this output and want to speed it up further.
 CONFIGURATION
 -------------
 
+include::includes/cmd-config-section-all.txt[]
+
 include::config/fsck.txt[]
 
 DISCUSSION

Documentation/git-gc.txt

@@ -110,8 +110,7 @@ users and their repositories.
 CONFIGURATION
 -------------
 
-The below documentation is the same as what's found in
-linkgit:git-config[1]:
+include::includes/cmd-config-section-all.txt[]
 
 include::config/gc.txt[]
 

Documentation/git-imap-send.txt

@@ -54,6 +54,8 @@ CONFIGURATION
 To use the tool, `imap.folder` and either `imap.tunnel` or `imap.host` must be set
 to appropriate values.
 
+include::includes/cmd-config-section-rest.txt[]
+
 include::config/imap.txt[]
 
 EXAMPLES

Documentation/git-merge.txt

@@ -386,13 +386,16 @@ include::merge-strategies.txt[]
 
 CONFIGURATION
 -------------
-include::config/merge.txt[]
 
 branch.<name>.mergeOptions::
 	Sets default options for merging into branch <name>. The syntax and
 	supported options are the same as those of 'git merge', but option
 	values containing whitespace characters are currently not supported.
 
+include::includes/cmd-config-section-rest.txt[]
+
+include::config/merge.txt[]
+
 SEE ALSO
 --------
 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],

Documentation/git-mergetool.txt

@@ -102,6 +102,9 @@ success of the resolution after the custom tool has exited.
 CONFIGURATION
 -------------
 :git-mergetool: 1
+
+include::includes/cmd-config-section-all.txt[]
+
 include::config/mergetool.txt[]
 
 TEMPORARY FILES

Documentation/git-rebase.txt

@@ -1252,6 +1252,8 @@ merge cmake
 CONFIGURATION
 -------------
 
+include::includes/cmd-config-section-all.txt[]
+
 include::config/rebase.txt[]
 include::config/sequencer.txt[]
 

Documentation/includes/cmd-config-section-all.txt

@@ -0,0 +1,3 @@
+Everything below this line in this section is selectively included
+from the linkgit:git-config[1] documentation. The content is the same
+as what's found there:

Documentation/includes/cmd-config-section-rest.txt

@@ -0,0 +1,3 @@
+Everything above this line in this section isn't included from the
+linkgit:git-config[1] documentation. The content that follows is the
+same as what's found there: