When running @welcomebot help, any users or subteams mentioned should be escaped

[lucymhdavies]

This will allow a @welcomebot help in a channel, without notifying all those users every time.

For example, if the config for a channel contains:

<!subteam^S0ABCDEFG|admins>

Simplest way to escape that would be to enclose it in backticks.

Same for users, which look like this:

<@U01ABCDEF|lucy.davinhart>

In both cases, I think that the |foo part is optional, but if one is provided, we could replace something like

<@U01ABCDEF|lucy.davinhart> --> (@lucy.davinhart)