Update CONTRIBUTING.md with details what versions of browsers should be used etc.

[jakub-g]

It would be good IMO to document in CONTRIBUTING.md what versions are expected to be provided in the compat data

• Edge shows two versions when you go to its Settings screen, the browser itself like Microsoft Edge 42.17134.1.0 and the engine version like Microsoft EdgeHTML 17.17134. It seems that the latter is used on MDN (Edge 17)
• When it comes to mobile Safari, should the version of Safari or version of iOS be provided? This is not clear (they are not always in sync, for example Safari 11.1 is shipped in iOS 11.3 -> seems that Safari version is used
• Whether versions of Safari should be like 11.0 or 11 -> seems that 11 format is used

(Also on MDN itself, maybe when you hover over those browsers, it should say which version are we talking about).

WDYT?

[queengooborg]

You've brought up some really good points, and these parts can come off as confusing. I'll start tackling this one!

Edge shows two versions when you go to its Settings screen, the browser itself like Microsoft Edge 42.17134.1.0 and the engine version like Microsoft EdgeHTML 17.17134. It seems that the latter is used on MDN (Edge 17)

This, I intend to resolve in #3166.

When it comes to mobile Safari, should the version of Safari or version of iOS be provided? This is not clear (they are not always in sync, for example Safari 11.1 is shipped in iOS 11.3 -> seems that Safari version is used

We've been using the Safari versions, but Apple states that it should be the iOS version.

Whether versions of Safari should be like 11.0 or 11 -> seems that 11 format is used

This is correct, and should definitely be addressed in the documentation.