[Docs] Restart Claude Code to load new plugins

### Problem

We don't explicitly say that the user will need to restart Claude Code after following our instructions. But we should!

### Proposed solution

Add this to the README:

```
Restart Claude Code to load new plugins.
```

And/or something like this:

Run `claude --continue` or `claude --resume` to resume a conversation:
```shell
claude --continue
```