Make Observable more Social: Add Hashtags to Notebooks

[Daynex]

Is your feature request related to a problem? Please describe. I currently know of 3 ways to find exciting notebooks that interest me:

1. Use the 4 options available in the Explore tab.
2. Use the search feature.
3. Look at profiles of people I know and check if they have new notebooks.

By offering to add tags (hashtags) to notebooks it will be easier to find notebooks that interest me as well as to follow topics and promote notebooks.

Describe the solution you'd like

1. It would be amazing if one could add hashtags, such as #womanshistorymonth to notebooks.
2. As a result of hashtags it would be fantastic to subscribe or query by a hashtag.
3. It might also help the Observable team in categorising notebooks and to make organisation around competitions and events easier, such as with the current Women in DataViz Event

Describe alternatives you've considered Searching by keywords.

[CobusT]

Notebooks can now have tags! We are still working on the ability to search by tag.

https://observablehq.com/@observablehq/tags

[CobusT]

You can now search using hashtags... https://observablehq.com/@observablehq/searching-on-observable#users1