Fix git remote show and git ls-remote args

Both are optional and should be square brackets.

Author: crd

book/03-git-branching/sections/remote-branches.asc

@@ -3,7 +3,7 @@
 
 (((branches, remote)))(((references, remote)))
 Remote references are references (pointers) in your remote repositories, including branches, tags, and so on.
-You can get a full list of remote references explicitly with `git ls-remote (remote)`, or `git remote show (remote)` for remote branches as well as more information.
+You can get a full list of remote references explicitly with `git ls-remote [remote]`, or `git remote show [remote]` for remote branches as well as more information.
 Nevertheless, a more common way is to take advantage of remote-tracking branches.
 
 Remote-tracking branches are references to the state of remote branches.