Feature - Show message for invalid parameters

**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.

Start by locating the React component's handling of invalid props and the GitHub API error response. Implement messages that identify an unavailable username or the invalid prop and expected input, then verify each invalid-prop case displays the appropriate message.

Written by the indexing model from the issue text.