Update docs on pystow/sqlite cache management

[cmungall]

We have a FAQ entry "My cached SQLite ontology is out of date"
https://incatools.github.io/ontology-access-kit/faq/troubleshooting.html#my-cached-sqlite-ontology-is-out-of-date

This recommends low-level navigating to the pystow .data directly and explicitly clearing old .db files.

However, since 0.6.17 we have had much better cache management tools captured in the release notes here:

https://github.com/INCATools/ontology-access-kit/releases/tag/v0.6.17

We have two commands:

• https://incatools.github.io/ontology-access-kit/cli.html#runoak-cache-ls
• https://incatools.github.io/ontology-access-kit/cli.html#runoak-cache-clear

And also a global option:

--caching CACHE-POLICY Set the cache management policy