Note on backwards compatibility

[dichotommy]

Add note on backwards compatibility in guides/advanced_guides/installation.md#updating-meilisearch. Other relevant locations in the docs?
Something like this:
"MeiliSearch is in beta! Backwards compatibility is a planned feature for our official release. For now, you can use the dumps feature to maintain your database between updates."

Related to #1152

[bidoubiwa]

I dont think there is another fitting place. Maybe in the introduction?
https://docs.meilisearch.com/guides/introduction/

[dichotommy]

Fixed by #702