design specifications and Gitlab – best practices

I am not sure this is the right place to ask but there goes.

What are the best practices regarding specifications and Gitlab?
The question of design/technical documentation location was brought up in a meeting.
Is Gitlab a good place to store those documents?
The main worry was about if/when we decide to let go of Gitlab, and if it would become an annoyance to have all docs/diagrams stored in there.

Optional question: where can I see general best practices about those processes? I am looking for opinions based on experience, rather than untested theories.