Helping with Documentation: Update old BPO info

[hugovk]

Update redundant BPO info now we're using GitHub issues.

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I'm not sure if we still need this bullet point?

-* check to see if there is a paperclip or `octocat`_ icon at the end of the
-  issue's title column.  If there is, then someone has already created a pull
+* check to see if there is pull request icon to the right of the
+  issue's title.  If there is, then someone has already created a pull
   request for the issue.

[JelleZijlstra]

I think the bullet point is still useful; I've seen people create PRs for issues that already have one.

[CAM-Gerlach]

It's good to update this, though I did have a couple comments/suggestions

[CAM-Gerlach]

LGTM, thanks @hugovk