Feature - Show message for invalid parameters

[jangerhard]

Is your feature request related to a problem? Please describe.
Make sure the component shows a nice-looking message if the component has invalid props, which will be returned from the Github API.

Describe the solution you'd like
If the error message states that the username cannot be located, then show a message stating which user cannot be found. If other props fail, state which and explain what kind of input is expected.