Update README.md

[LouisCAD]

KMP is no longer in beta: https://kotlinlang.org/docs/components-stability.html#kotlin-multiplatform

[cla-bot]

Realm welcomes all contributions! The only requirement we have is that, like many other projects, we need to have a Contributor License Agreement (CLA) in place before we can accept any external code. Our own CLA is a modified version of the Apache Software Foundation’s CLA. Our records show that CLA has not been signed by @LouisCAD. Please submit your CLA electronically using our Google form so we can accept your submissions. After signing the CLA you can recheck this PR with a @cla-bot check comment. The GitHub usernames you file there will need to match that of your Pull Requests. If you have any questions or cannot file the CLA electronically, make a comment here and we will be happy to help you out.

[LouisCAD]

Is the CLA really necessary for such a small scoped change?

[clementetb]

would you mind change the base to community?

[LouisCAD]

@clementetb Done