2013-06-24-wise/test_install.html: HTML markup and indentation

* Add missing <p> and <code> tags.
* Close unclosed tags (e.g. '<p>...' -> '<p>...</p>').
* Consistently indent nested tag content with spaces.
* Remove trailing whitespace.

Due to the whitespace changes, the unified diff looks pretty
intrusive.  If you want to focus on the substantive changes, use:

  $ git diff --word-diff=color