Add tags when posting notes

To help with local search and filtering, it would be cool if damus supported adding tags when posting. These could be hashtags ala [NIP12](https://github.com/fiatjaf/nostr/blob/master/nips/12.md) or something else.

Users can than filter on certain tags for users. If they only want to follow a users posts about bitcoin for example, you could tag the post with bitcoin.