Unity: Clarify expectations of SDK update when new releases of Unity are made

[bruno-garcia]

SDK

Unity SDK

Description

It's very common for Unity customers to install the SDK once, and never update it.
They often update Unity itself, but not the SDK, which ends up causing issues when Unity introduces changes that are incompatible with Sentry.

Suggested Solution

Add a note to the docs stating that when updating Unity, users should also update Sentry to the latest version to get all bug fixes and compatibility changes introduced by Sentry.