Documentation/urls.txt: Use substitution to escape square brackets

This changes "[user@]" to use {startsb} and {endsb} to insert [ and ],
similar to how {caret} is used in git-rev-parse.txt.

[jc: Removed a well-intentioned comment that broke the final
 formatting from the original patch.  While we are at it,
 updated the paragraph that claims to be equivalent to the
 section that was updated earlier without making matching
 changes.]

Signed-off-by: Jonas Fonseca <fonseca@diku.dk>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/asciidoc.conf

@@ -9,6 +9,8 @@
 
 [attributes]
 caret=^
+startsb=[
+endsb=]
 
 ifdef::backend-docbook[]
 [gitlink-inlinemacro]

Documentation/urls.txt

@@ -10,20 +10,21 @@ to name the remote repository:
 - https://host.xz/path/to/repo.git/
 - git://host.xz/path/to/repo.git/
 - git://host.xz/~user/path/to/repo.git/
-- ssh://+++[user@+++]host.xz/path/to/repo.git/
-- ssh://+++[user@+++]host.xz/~user/path/to/repo.git/
-- ssh://+++[user@+++]host.xz/~/path/to/repo.git
+- ssh://{startsb}user@{endsb}host.xz/path/to/repo.git/
+- ssh://{startsb}user@{endsb}host.xz/~user/path/to/repo.git/
+- ssh://{startsb}user@{endsb}host.xz/~/path/to/repo.git
 ===============================================================
 
-SSH is the default transport protocol and also supports an
-scp-like syntax.  Both syntaxes support username expansion,
+SSH is the default transport protocol.  You can optionally specify
+which user to log-in as, and an alternate, scp-like syntax is also
+supported.  Both syntaxes support username expansion,
 as does the native git protocol. The following three are
 identical to the last three above, respectively:
 
 ===============================================================
-- host.xz:/path/to/repo.git/
-- host.xz:~user/path/to/repo.git/
-- host.xz:path/to/repo.git
+- {startsb}user@{endsb}host.xz:/path/to/repo.git/
+- {startsb}user@{endsb}host.xz:~user/path/to/repo.git/
+- {startsb}user@{endsb}host.xz:path/to/repo.git
 ===============================================================
 
 To sync with a local directory, use: