Minor corrections to Trigger guide

Mostly fixes typos and improves the formatting such that the formatting on the validation.md page is a bit more legible in both light & dark mode (using more neutral shades).

A couple of slightly more substantial additions on combohypo.md. @tamartin, would you agree with the phrasing on the jet steps, and on the 2-body variable calculations?

There were a couple of other questions I had:

1. On the top level page, we link to runHLT in 24.0 but many other places point to main. To be consistent, should we link 24.0 to point to production code or main for future-proofing?
2. Not sure if this change on combohypo.md is correct (L90):

If the feature is itself and ^an RoI, and that RoI is flagged as full-scan.

3. On monitoring.md, we have the cryptic phrase

* __all__ variables computed by reconstruction and hypo algorithms (not tools) and __monitored__ should be monitored.

This looks like __monitored__ should be replaced with something, or omitted.