Document lack of support for [email protected] notation

[jsoref]

GitHub's CODEOWNERS files support this notation:

In most cases, you can also refer to a user by an email address that has been added to their account on GitHub.com, for example [email protected].

https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners#codeowners-syntax

The code in trimUsername will do something inconsistent with GitHub's behavior for [email protected]:

robot-overlord/src/utils.ts

Lines 121 to 122 in e60c44e

	export const trimUsername = (original: string): string => {
	const match = original.match(/[\w-/]+/)