[docs][`pouchdb-find`] Obsolete reference to selector documentation (Mango queries)

The our link I'm discussing is [CouchDB _find documentation](https://docs.couchdb.org/en/stable/api/database/find.html): https://github.com/pouchdb/pouchdb/blob/f2c665a2a885437b9cea80dda62c02a93a137c1e/docs/_guides/mango-queries.md?plain=1#L348

Problem:

Couchdb changed the address of the documentation page in version 3.5. It was

https://docs.couchdb.org/en/stable/api/database/find.html

now in 3.5 it's

https://docs.couchdb.org/en/stable/ddocs/mango.html

Proposed solution:

So I suggest that we should either change the link to version 3.4

https://docs.couchdb.org/en/3.4.3.post1/api/database/find.html

or refer to the new address in 3.5

https://docs.couchdb.org/en/stable/ddocs/mango.html

P.S. I haven't watched for differences between versions (if any), so I don't know which link to recommend keeping.