Missing documentation for ` select * from idx.files`

Nobody has claimed this yet.

In https://github.com/manticoresoftware/manticoresearch/issues/821 [sanikolaev](https://github.com/sanikolaev) said:

> use select * from idx.files to get list of index files (it works for plain/pq indexes too)

Wwhere is this documented? Not seen the .files table before? Are there any more of these?
Dont find it listed here: https://manual.manticoresearch.com/Listing_indexes Seems it should be documented along side DESCRIBE

Also, seems liek this files listing would be could place to include the modification time too
https://github.com/manticoresoftware/manticoresearch/issues/69

Second aside, really liked the single page sphinx documentation page. Could Ctrl-F to find anything. Can't do that with new docs. can sort of grep in the manual/ folder, but it not as convenient.

~/manticoresearch/manual$ find -type f -name "*.md" | xargs grep .files -F

doesn't find anything!

Start with the manual page for Listing indexes and search manual/ for existing index-file documentation. Document how to use `select * from idx.files` and clarify whether modification times or related tables are in scope; the work is done when users can find and understand this query in the manual.

Written by the indexing model from the issue text.