Fix gitbook so that click documentation is viewable

[emprzy]

Describe your changes.

This pull request:

• Updates the gitbook SUMMARY.md file to properly tab click documentation files
• Adds a README.md to the gitbook/technical-reference/click-commands dir
• Deletes extraneous documentation refs and docs

Does this pull request make any user interface changes? If so please describe.

No user interface changes.

What does your pull request address? Tag relevant issues.

This pull request addresses GH #610

[emprzy]

Important note ⚠️
The original idea (from #545) for the click documentation would that it would be auto-updating. That is, there is a step in the gempyor-CI workflow that builds this documentation, so that when any info within the source code for any of the commands changes, the documentation will reflect that. However, with the command names hard-coded into SUMMARY.md, entirely new or deleted commands will not be automatically reflected in the documentation and will require manual updates. Two options:

1. I can add dynamic md-writing functionality somewhere so that the SUMMARY.md gets re-written if there are new commands, but I don't really think there should be re-writes of the summary markdown file just to maintain something like that.
2. Leave it as-is and expect devs to update the documentation if they add or delete a command. This is probably the best option.

Let me know your thoughts @TimothyWillard @pearsonca