Add some less brief tips'n'tricks to eg. doc/TRICKS

https://github.com/openwall/john/issues/4403#issuecomment-706755482

This file would be for tips'n'tricks regarding actual use of Jumbo, as opposed to building it etc.

Candidates for this doc file (please fill in! Just amend this post if you've got the privileges):

• Using FIFOs: Pros, cons, caveats.
• Piping john -stdout | john -stdin. Why, when?
• Advanced use of --format option (https://github.com/openwall/john/pull/4395#issuecomment-703144071).
• Advanced use of --salt option (also mention NoLoaderDupeCheck which might be relevant for that situation).
• Advanced use of --single mode (many sparsely documented options available).
• There might be some other good tricks mentioned in #1706 or linked from it (the context at the time was trying to handle the Ashley Madison leak, a hefty number of super slow and correctly salted hashes).
• Perhaps some stuff from the Openwall wiki.
• Introduce pass_gen.pl for creating datasets for testing.
• Difference (in order) between eg. ?d and [0-9] in masks.

Start with doc/TRICKS and review the linked discussion in #4403, plus the candidates from #1706, the Openwall wiki, and PR #4395. Select and document practical Jumbo usage tips such as FIFOs, piping, advanced options, pass_gen.pl, and mask syntax, with the completed document covering the agreed topics.