Automate generation of README values documentation

**Is your feature request related to a problem? Please describe.**
As discussed in #80 , keeping `values.yaml` in sync with `README.md` can be tricky. As a result, a tool called [`helm-docs`](https://github.com/norwoodj/helm-docs) has been developed that uses go-templating to auto-generate the README.md

**Describe the solution you'd like**
Use GitHub Actions / CI to auto-generate `helm-docs` output / keep the README.md documentation up to date with `values.yaml`

**Describe alternatives you've considered**
Manual maintenance as is currently done

**Additional context**
I have started on an implementation of this, which has generated some questions:

- `couchdb-helm` currently displays "selections" of values. i.e. "these values are for XYZ, these are for ABC". Is this desirable to maintain? `helm-docs` does not currently support this idea, but I have [created an issue to track doing so](https://github.com/norwoodj/helm-docs/issues/156), because it seems nice
- Unfortunately, if this is desirable, the workaround is a little gross in the short term. I am happy to PR for review based on preference of output
- An example display of "all values in a big table together" is [here](https://github.com/colearendt/helm/tree/main/charts/postgrest#values)
- Currently the documentation in `README.md` is quite concise (i.e. one sentence) and docs in `values.yaml` are _quite thorough_. If auto-generating, is it OK for README.md to become more verbose in line with `values.yaml`?