Add note in docs linking to local datastore issue

[Jawnnypoo]

It is important for SDK users to understand the drawbacks of using Local Datastore when using the SDK. I think that we need to have a link to the open issue directly in the docs, so there are no surprises for users once they go down the route of using local datastore in their project. https://github.com/parse-community/Parse-SDK-Android/issues/279

[mtrezza]

@TomWFox As the "docs expert", what is your opinion on linking Github issues directly in the docs? Anything we should consider? Or should we rather extract the gist from the issue discussion and add that to the docs, so people don't have to read through the whole issue thread (which may contain incorrect comments and presumptions from non-team members) and we keep the docs concise?

[TomWFox]

Seems like a good idea, probably for the iOS guide too.

I would say extracting the key points for the docs would be preferable but you could also provide a link for those who want to see the whole thread.

[mtrezza]

@Jawnnypoo Do you think you could just briefly mention the key issue with the local datastore in the docs, in addition to the issue link?

[mtrezza]

I can then open an iOS PR to add the same comment there (if the same problem exists), thanks @TomWFox for suggesting.