Add note to use Personal Forks and not Organization forks for PR's

Paper will routinely modify your PR for you to rebase it on latest or take care of any minor nitpicks that we can
just solve for you instead of making you go back for a trivial item.

However, if you use an Organization for the PR, this prevents Paper from doing this, and will require us to manually
merge it and close the PR instead of it being marked as the purple merged.

We much prefer to have merged PR's show as merged, so please do not use organizations repo's for PR as GitHub sadly
does not support maintainers pushing to them.

See [https://github.com/isaacs/github/issues/1681](https://github.com/isaacs/github/issues/1681)

CONTRIBUTING.md

@@ -2,6 +2,18 @@ Contributing to Paper
 ==========================
 PaperMC has a very lenient policy towards PRs, but would prefer that you try and adhere to the following guidelines.
 
+## Use a Personal Fork and not Organization
+Paper will routinely modify your PR for you to rebase it on latest or take care of any minor nitpicks that we can
+just solve for you instead of making you go back for a trivial item.
+
+However, if you use an Organization for the PR, this prevents Paper from doing this, and will require us to manually
+merge it and close the PR instead of it being marked as the purple merged.
+
+We much prefer to have merged PR's show as merged, so please do not use organizations repo's for PR as GitHub sadly
+does not support maintainers pushing to them.
+
+See [https://github.com/isaacs/github/issues/1681](https://github.com/isaacs/github/issues/1681)
+
 ## Understanding Patches
 Patches to Paper are very simple, but center around the directories 'Paper-API' and 'Paper-Server'