Document the procedure of upgrading the `kotlinx.coroutines` repository to the new Kotlin

[dkhalanskyjb]

We do this mindlessly, but it's getting a bit complicated, so let's document what exactly one has to do to upgrade to the new Kotlin version.

• The changes from Update Kotlin to 2.2.0 #4485
• The change from Update Kotlin to 2.2.0 - update the playground link to 2.2.0 #4496
• Something else?