docs: Fix and expand module config docs
docs: Fix and expand module config docs

- Add a missing rebase_path() call and adjust some wording.
- Include the rationale for choosing this config patten over
  alternatives.

Change-Id: I775dc1c7a43e1cb5d0e4ad7ea0afbe81c18374b1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/32440
Pigweed-Auto-Submit: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Reviewed-by: Ewout van Bekkum <638f134dbc68778d6b859fb04a64baea2b00b021@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed