Slight adjustment to rule_priority in the Fares Implementation Guide

[skalexch]

No description provided.

[skalexch]

After having reviewed the guide, we do not need to update anything major except what's in this PR. We do not say anything incorrect or dangerous in rule_priority.
We also kept things simple with transfers so the semantics clarification does not induce any change in the guide on our side.
Tagging @abigailmbd for documentation review and @Sergiodero to make sure what I added is not too complex.

Next step in the guide is to draft new content related to new and upcoming proposals:

• cEMV support
• Area Sets + Leg Join
  These will appear in their own PRs.

[skalexch]

@Sergiodero should I change "predicates" to "conditions"?

[abigailmbd]

The changes look good, though I would agree that "conditions" is clearer here than "predicates."

[Sergiodero]

100% agree with using "conditions" over "predicates", other than that LGTM!

[Sergiodero]

Also, just flagging that we currently do not have translations for this guide. We should add this to the backlog once the migration to the resources section is completed.