Change Google Doc references to published versions if they are not meant for editing

[LukasWallrich]

In some places, we link to Google Docs to share information - particularly "Get involved" - let's link to published versions there, rather than the docs themselves - that allows us to add comments without them being visible on the page, and looks more professional.

Here the get involved link to replace the current: https://docs.google.com/document/d/e/2PACX-1vR_OKOxDlrbPcXn6SZLYlq19139ofcYDInBu9E392jWG5yzbp2VjF7E1_fwtzTz4Wxo9i4ddHZTbHfT/pub

Not sure how many others there are