Update documentation to include new full-text search keywords

[quinncomendant]

Steps to reproduce the problem

The Mastodon documentation for Search mentions “Admins may optionally install full-text search” but it doesn't list the new keyword operators that were added (has:, is:, from:, before:, etc).

Expected behaviour

The documentation should contain all search parameters

Actual behaviour

The documentation lacks this info

Detailed description

No response

Mastodon instance

No response

Mastodon version

No response

Technical details

No response

[trwnh]

please file this on https://github.com/mastodon/documentation

[eiland-asbl]

Also, no information available about (how to use) search operators like AND OR & NOT.

And it seems not possible to pin searches?

[vmstan]

Duplicate of #1286