Add a hint for integrating custom token

[Calla-Ji]

Is your feature request related to a problem? Please describe.
Until Julien pointed me towards it I never realized we can add custom tokens to our locks.

Describe the solution you'd like
Maybe adding a short description to the coin selection field, similar to the Network one, pointing out that "Custom Token can be integrated," will help make users more aware.

Describe alternatives you've considered
None

Additional context