Instructions regarding settings.local.php seem to be missing from logical places both in the User Guide and the Community Docs. I got some pointers on drupal.stackexchange.com that helped redirect me.
Some of the platform-specific pages in the local-server-setup section of the guide mention the file, but (I believe the following should be rectified – am I understanding correctly?)
– the description of settings.local.php is not included for each platform
– the use of settings.local.php in place of settings.php should not be a platform-specific concern
– an actual prompt to adopt the practice for local dev appears to be missing regarding using settings.local.php in place of settings.php
For reference, the Unix instructions within the Linux section seem to have the most info on settings.local.php. The MacOS section does not mention it at all.
Am I overlooking docs that already exist, or can I assist with adding them? It would seem logical to add basics to the “local” section of Before a Drupal 8 installation.