SpeckleGSA docs

Hey @dimitrie and @teocomi - over at SpeckleGSA we are wanting to create some more extensive documentation. We were thinking that it might be easier just to add a link to our docs on the main speckle site for the gsa client. Are you happy with that? I can submit a pull request implementing the change to the main site when our docs site is ready.

Hi @HughGrovesArup! For sure, go ahead!