Added 'RFC and Voting' to CONTRIBUTING.md
Fix typo, added PR: Request for Comments label
Fixed text typo
Update CONTRIBUTING.md

Smoothed out wording, fix grammar.
Merge pull request #2113 from tnpxxsheepdog/rfc-rfc-and-voting

Update CONTRIBUTING.md
Fixed missing whitespace
Changed RFC label
Added RFC ready status, added new label to label list
Merge pull request #2112 from PocketMine/rfc-rfc-and-voting

RFC and Voting