Epic/collection thread: Documentation updates

There are various documentation updates to make, so I'm going to collect them here in a single issue (that can then be addressed via one or multiple PRs).

## Update documentation for users

- [ ] The one sentence "This documentation was created to help E3SM users find data officially released model data from the E3SM simulations campaigns as well as reproduce simulations." on the [home page](https://docs.e3sm.org/e3sm_data_docs/_build/html/index.html) could use refining.
- [ ] While the [v3 table](https://docs.e3sm.org/e3sm_data_docs/_build/html/v3/CoupledSystem/simulation_data/simulation_table.html) has the direct URL to access HPSS paths, some other simulations do not. For example, the [v2 water cycle table](https://docs.e3sm.org/e3sm_data_docs/_build/html/v2/WaterCycle/simulation_data/simulation_table.html) does not have such a column. Furthermore, as noted in #72, something is wrong with the web path.
- [ ] #30 / #51 -- replace the `rst` tables with `csv` tables, which should be easier to maintain.

## Update documentation for developers

- [ ] Use details from https://github.com/E3SM-Project/e3sm_data_docs/discussions/71 to fill out `main/README.md` and `main/utils/README.md`