doc: enforce placeholders in documentation

Any string that is not meant to be used verbatim in the documentation
should be marked as a placeholder.

Signed-off-by: Jean-Noël Avila <jn.avila@free.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/diff-options.txt

@@ -299,7 +299,7 @@ and accumulating child directory counts in the parent directories:
 	Synonym for --dirstat=cumulative
 
 --dirstat-by-file[=<param1,param2>...]::
-	Synonym for --dirstat=files,param1,param2...
+	Synonym for --dirstat=files,<param1>,<param2>...
 
 --summary::
 	Output a condensed summary of extended header information

Documentation/git-config.txt

@@ -103,11 +103,11 @@ OPTIONS
 	names are not.
 
 --get-urlmatch <name> <URL>::
-	When given a two-part name section.key, the value for
-	section.<URL>.key whose <URL> part matches the best to the
+	When given a two-part <name> as <section>.<key>, the value for
+	<section>.<URL>.<key> whose <URL> part matches the best to the
 	given URL is returned (if no such key exists, the value for
-	section.key is used as a fallback).  When given just the
-	section as name, do so for all the keys in the section and
+	<section>.<key> is used as a fallback).  When given just the
+	<section> as name, do so for all the keys in the section and
 	list them.  Returns error code 1 if no value is found.
 
 --global::

Documentation/git-daemon.txt

@@ -141,8 +141,8 @@ otherwise `stderr`.
 	specified with no parameter, a request to
 	git://host/{tilde}alice/foo is taken as a request to access
 	'foo' repository in the home directory of user `alice`.
-	If `--user-path=path` is specified, the same request is
-	taken as a request to access `path/foo` repository in
+	If `--user-path=<path>` is specified, the same request is
+	taken as a request to access `<path>/foo` repository in
 	the home directory of user `alice`.
 
 --verbose::

Documentation/git-difftool.txt

@@ -90,7 +90,7 @@ instead.  `--no-symlinks` is the default on Windows.
 --extcmd=<command>::
 	Specify a custom command for viewing diffs.
 	'git-difftool' ignores the configured defaults and runs
-	`$command $LOCAL $REMOTE` when this option is specified.
+	`<command> $LOCAL $REMOTE` when this option is specified.
 	Additionally, `$BASE` is set in the environment.
 
 -g::

Documentation/git.txt

@@ -202,7 +202,7 @@ If you just want to run git as if it was started in `<path>` then use
 	Do not perform optional operations that require locks. This is
 	equivalent to setting the `GIT_OPTIONAL_LOCKS` to `0`.
 
---list-cmds=group[,group...]::
+--list-cmds=<group>[,<group>...]::
 	List commands by group. This is an internal/experimental
 	option and may change or be removed in the future. Supported
 	groups are: builtins, parseopt (builtin commands that use