Fix mu-init manpage markup

[c0dev0id]

Hi,

The manpage markup in mu-init is broken and renders like this when escape sequences are enabled:

<my-email-address> can be either a plain e-mail address (such as
foo@example.com), or a regular-expression (of the 'Basic POSIX'
flavor), wrapped in 0

This PR fixes the markup to what I think was meant. Also, I think the second '/' was missing in the wrapped regex email address notation.

With this fix, it reads like:

<my-email-address> can be either a plain e-mail address (such as
foo@example.com), or a regular-expression (of the 'Basic POSIX'
flavor), wrapped in / (such as /foo-.*@example\.com/).

The '/' as well as '/foo-.*@example.com/' are bold.

[djcb]

Merged, thanks.