RFE: document HCL config key names along side CLI arguments

#### Feature Description

It should be documented when the HCL config key name is not the same as the
command line argument. `-node` vs `node_name`, `-join` vs `start_join`.

These differences should be highlighted clearly in the documentation beside their corresponding
CLI arguments.

#### Use Case(s)

1. Converting CLI arguments to HCL configuration
1. Reduce confusion: it is unexpected and confusing to see `invalid config key join` or `invalid config key node`

No files or tests are named. Locate the documentation for the `-node`/`node_name` and `-join`/`start_join` options, then review nearby CLI arguments for other differing HCL keys. Done means each mismatch is clearly documented beside its corresponding argument.

Written by the indexing model from the issue text.