ISSUE-75: Added example on skipping settings.php generation.

[vishalkhode1]

Motivation
Added an example which developers can follow to skip settings.php generation for certain use cases.

Proposed changes
Example file added showing on how to skip settings.php generation.

Alternatives considered
The Alternative thought be provide the similar way that BLT provides, but want to keep it simple and extensible, so ideal approach could be giving flexibility to developers, where they can create their own library/drush command and add their own checks to skip the settings.php generation logic.

Testing steps

1. Include the example drush command in project.
2. Set the environment variable i.e CI=true.
3. Run the command drush drs:init:settings and you'll notice generation of settings.php is skipped..

[apathak18]