Add a don't to CONTRIBUTING about merge messages

Also updated the wiki with an example message to allay any confusion
about avoiding the default merge message.

http://r-7.co/MSF-Landing-PRs

Also fix an italics where it should have been bold.

Author: Tod Beardsley

CONTRIBUTING.md

@@ -37,8 +37,10 @@ and Metasploit's [Common Coding Mistakes](https://github.com/rapid7/metasploit-f
 ## Code Contributions
 
 * **Do** stick to the [Ruby style guide](https://github.com/bbatsov/ruby-style-guide).
-* *Do* get [Rubocop](https://rubygems.org/search?query=rubocop) relatively quiet against the code you are adding or modifying.
+* **Do** get [Rubocop](https://rubygems.org/search?query=rubocop) relatively quiet against the code you are adding or modifying.
 * **Do** follow the [50/72 rule](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html) for Git commit messages.
+* **Don't** use the default merge messages when merging from other
+   branches.
 * **Do** create a [topic branch](http://git-scm.com/book/en/Git-Branching-Branching-Workflows#Topic-Branches) to work on instead of working directly on `master`.
 
 ### Pull Requests