Document that alternate dictionariy files are not enabled by default

[Techcable]

Description

I wanted to contribute spelling corrections for 'loosing' and 'seperate', which are corrected by codespell 2.4.1 but not typos-cli 1.33.1.

I found these spellings present in crates/wikipedia-dict/assets/dictionary.txt, and was confused they were not being corrected. I had to search the issue tracker to learn these dictionaries are "included mostly for comparison"

Please document this in ⁣CONTRIBUTING.md. If the dictionary files support comments, then a notice at the top of the file would also be very helpful.

[epage]

CONTRIBUTING.md specifically says what file is to be updated: https://github.com/crate-ci/typos/blob/master/CONTRIBUTING.md#updating-the-dictionary

The fact that other files exist seems less of a concern after that to me.