doc/contribute: fix some tags, remove extra space.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/7327048

doc/contribute.html

@@ -524,6 +524,7 @@ Once the CL has been submitted, the next time you run <code>hg sync</code>
 it will be removed from your local pending list. Occasionally the pending list
 can get out of sync leaving stale references to closed or abandoned CLs.
 You can use <code>hg change -D 99999</code> to remove the reference to CL 99999.
+</p>
 
 <h3>Submit the change after the review</h3>
 
@@ -543,6 +544,7 @@ $ hg clpatch 99999
 $ hg submit 99999
 </pre>
 
+<p>
 The <code>submit</code> command submits the code.  You will be listed as the
 author, but the change message will also indicate who the committer was.
 Your local client will notice that the change has been submitted
@@ -566,8 +568,7 @@ in the repository.
 
 <p>
 If your local copy of the repository is out of date,
-<code>hg submit</code>
-will refuse the change:
+<code>hg submit</code> will refuse the change:
 </p>
 
 <pre>