doc/contribute: add necessary <code> tags, remove an extra close parenthesis.

Change-Id: I7238ae84d637534a345e5d077b8c63466148bd75
Reviewed-on: https://go-review.googlesource.com/1521Reviewed-by: Russ Cox <rsc@golang.org>

doc/contribute.html

@@ -154,7 +154,7 @@ Git, note that you still need the commit hooks that the git-codereview command
 configures; those hooks add a Gerrit <code>Change-Id</code> line to the commit
 message and check that all Go source files have been formatted with gofmt. Even
 if you intend to use plain Git for daily work, install the hooks in a new Git
-checkout by running <code>git-codereview</code> <code>hooks</code>).
+checkout by running <code>git-codereview</code> <code>hooks</code>.
 </p>
 
 <h3>Set up git aliases</h3>
@@ -461,7 +461,7 @@ $ git sync
 </pre>
 
 <p>
-(In git terms, git sync runs
+(In git terms, <code>git</code> <code>sync</code> runs
 <code>git</code> <code>pull</code> <code>-r</code>.)
 </p>