docs(common): more information on localization process

[mcdurdin]

docs/localization/README.md includes basic information on the localization process. Some questions that are unanswered for me from a developer perspective:

1. If I change a source language (English) string in the source will the change propagate automatically so other localizations will be updated?
2. What happens when I delete an source language (English) string? Do I need to update the localized versions of files in my PR?
3. Will adding a string in source language (English) cause that string to appear automatically in Crowdin? Will translators be notified?

[mcdurdin]

Note: if you remove a source language string in Android, but don't remove translations, then lint fails with an error like this:

10:18:34       /var/lib/TeamCity/work/30ffb35c1b6c4089/keyman/android/KMEA/app/src/main/res/values-in-rID/strings.xml:82: Error: "fatal_keyboard_error_short" is translated here but not found in default locale [ExtraTranslation]
10:18:34           <string name="fatal_keyboard_error_short" comment="Error in keyboard (keyboard ID::packageID for language).">      Error in keyboard %1$s:%2$s for %3$s language.</string>