Define SDK compatibility

[mtrezza]

Define SDK compatibility

[parse-github-assistant]

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[dplewis]

Add CI jobs which test against the major OS versions

This wouldn’t work as GitHub Actions only supports 5 concurrent jobs on MacOS images for the entire repo. A build matrix you want would take hours if not days to run. Not to mention actually implementing it.

Accordingly, a compatibility table needs to be added to the README

Github Badges for supported version have been added to the README, this should be enough.

The SDK also lacks a OS support policy

This is the current policy, no need to document it as it is standard everywhere.

1. Support the minimum versions Xcode supports.
2. Support the minimum versions allowed for specific iOS, macOS, tvOS, watchOS features.
3. Support the minimum versions allowed for dependencies.

[mtrezza]

A build matrix you want would take hours if not days to run. Not to mention actually implementing it.

The run time length is something we can solve with more runners. What's the challenge in the implementation? Is it more than just adding a matrix to the CI workflow like we do with Node.js for example?

Github Badges for supported version have been added to the README, this should be enough.

I wouldn't know how to interpret these badges. For example, what does the iOS 12.0 badge mean?

This is the current policy, no need to document it as it is standard everywhere.

We could still have a different policy, a developer currently can only guess what our policy is, so we need to define it. We do that in all other Parse SDKs.