Goal: extend README

[zolotokrylin]

Simple & clear description of the end user functions and "how to".
So anyone can read and understand how to operate it.

### Tasks
- [ ] https://github.com/holdex/pr-time-tracker/issues/266
- [ ] https://github.com/holdex/pr-time-tracker/issues/254
- [ ] https://github.com/holdex/pr-time-tracker/issues/255
- [ ] Problem: how-to explude certain users is missing (https://github.com/holdex/pr-time-tracker/blob/main/src/lib/server/trigger-dev/utils.ts#L26)
- [ ] Problem: "how-to install the app when it is a fork" is missing
- [ ] Problem: README doesn't explain the logic of how it works (adding goals to the oracle board)

[zolotokrylin]

@georgeciubotaru can you start dedicating 20 mins every day here, please?

[zolotokrylin]

We can do micro PRs and start enhancing README, so we don't make it everything or nothing...