Tweak.

CONTRIBUTING.md

 * Please make an individual commit for each suggestion in a separate pull request.
 * Use the following format for libraries: \[LIBRARY\]\(LINK\) - DESCRIPTION.
 * Prefix duplicate library names with their vendor or namespace followed by a space: Foo\Bar would be Foo Bar.
-* New categories or improvements to the existing categorisation are always welcome.
+* New categories, or improvements to the existing categorisation, are always welcome.
 * Please keep descriptions short, simple and unbiased. No buzzwords or marketing jargon please.
 * End all descriptions with a full stop/period.
 * Check your spelling and grammar.