Update docs: mention Docker requirement for db pull

[magentaqin]

What kind of change does this PR introduce?

Docs update for db pull--add Docker requirement.

What is the current behavior?

The supabase db pull command can fail with:

Cannot connect to the Docker daemon at unix:///.../docker.sock. Is the docker daemon running?

when Docker Desktop (or another Docker engine) is not running, but this requirement is not mentioned in the docs.

Related issue: #4507

What is the new behavior?

The supabase db pull docs now include a short note:

This command requires Docker Desktop (or a running Docker daemon), as it starts a local Postgres container to diff your remote schema.

This should make it clearer for new users that db pull depends on a running Docker daemon.

This is how it would be rendered:

Additional context

From my understanding, several other supabase db subcommands (e.g. db start, db dump) also rely on Docker to run Postgres or pg_dump in a container.

To keep this PR small and focused, I only updated the db pull docs. I’m happy to:

• add a more general note under the top-level supabase db section, and/or
• update the docs for the other db subcommands in a follow-up PR,

if you think that would be helpful.