Tweak guidelines.

CONTRIBUTING.md

 # Contribution Guidelines
 Please ensure your pull request adheres to the following guidelines:
 
-* Please search previous issues before making a suggestion, as it may be a duplicate.
-* Libraries that are PHP 5.3+, Composer installable, PSR compliant, and tested are preferred.
+* Please search previous suggestions before making a new one, as yours may be a duplicate.
+* Libraries that are PHP 5.3+, Composer-installable, PSR compliant, tested and documented are preferred.
 * Please make an individual pull request for each suggestion.
-* Please use the following format for libraries: \[LIBRARY\]\(LINK\) - DESCRIPTION.
-* Please prefix duplicate library names with their vendor or namespace followed by a space: Orno\DI would be Orno DI.
-* Please keep descriptions short and simple. 
-* Please end all descriptions with a full stop/period.
-* Please check your spelling and grammar.
+* Use the following format for libraries: \[LIBRARY\]\(LINK\) - DESCRIPTION.
+* Prefix duplicate library names with their vendor or namespace followed by a space: Orno\DI would be Orno DI.
+* Keep descriptions short and simple. 
+* End all descriptions with a full stop/period.
+* Check your spelling and grammar.
+* New categories, or improvements to the existing categorisaton are welcome.
 
-I try to open a suggestions issue each month, so feel free to add anything interesting to it. I’m also open to creating new categories or improving the existing ones.
+I try to open a ticket for suggestions each month, so feel free to add anything interesting to it.
 
 Thank you for your suggestions!