ADD: expanded documentation

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 86.23%. Comparing base (76fdb8e) to head (6b674e8).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #33 +/- ## ======================================= Coverage 86.23% 86.23% ======================================= Files 10 10 Lines 799 799 ======================================= Hits 689 689 Misses 110 110 ``` | [Flag](https://app.codecov.io/gh/esgf2-us/intake-esgf/pull/33/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=esgf2-us) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/esgf2-us/intake-esgf/pull/33/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=esgf2-us) | `86.23% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=esgf2-us#carryforward-flags-in-the-pull-request-comment) to find out more.

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