Deprecate "bin/phd ... --gently" and update documentation
Summary:
Ref T13321. Previously, the behavior was:
- `bin/phd stop --gently`: Stop all daemons with PID files that belong to the current instance.
- `bin/phd stop`: Stop all daemons with PID files that belong to the current instance. Complain if there are more processes.
- `bin/phd stop --force`: Stop all processes that look like daemons, ignoring instances.
The new behavior is:
- `bin/phd stop`: Stop all processes that look like daemons and belong to the current instance.
- `bin/phd stop --force`: Stop all processes that look like daemons, period.
Test Plan: Grep / documentation only.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13321
Differential Revision: https://secure.phabricator.com/D20602