Implement TBD commands, or update the docs

[carlosms]

The docs contain a few commands as TBD (To Be Done). We should either implement them, or remove them from the docs.

[smacker]

I would better implement them. Especially srcd components start. (I do src sql "select 1" now to start bblfsh or gitbase 😨 ) The only command that doesn't make much sense to me after all the changes we implemented: srcd components update