[pilot] `fastlane pilot distribute` is not documented

But CLI returns it as a valid option:

```
λ fastlane pilot help
[✔] 🚀
[13:18:29]: fastlane detected a Gemfile in the current directory
[13:18:29]: however it seems like you don't use `bundle exec`
[13:18:29]: to launch fastlane faster, please use
[13:18:29]:
[13:18:29]: $ bundle exec fastlane pilot help
[13:18:29]:
[13:18:29]: Get started using a Gemfile for fastlane https://docs.fastlane.tools/getting-started/ios/setup/#use-a-gemfile
pilot

The best way to manage your TestFlight testers and builds from your terminal

Commands: (* default)
add Adds new external tester(s) to a specific app (if given). This will also add an existing tester to an app.
builds Lists all builds for given application
distribute Distribute a previously uploaded binary to Apple TestFlight
export Exports all external testers to a CSV file
find Find tester(s) (internal or external) by their email address
help * Display global or [command] help documentation
import Import external testers from a CSV file called testers.csv
list Lists all registered testers, both internal and external
remove Remove external tester(s) by their email address
upload Uploads a new binary to Apple TestFlight

Global Options:
--verbose
-h, --help Display help documentation
-v, --version Display version information

Author:
Felix Krause

Website:
https://fastlane.tools

Documentation:
https://docs.fastlane.tools/actions/pilot/
```