Configurable intro screen title?

[decentral1se]

Following #329 would it be possible to configure the header on the initial glow screen?

For more context, I'm planning to run glow in a pubnix & would like to use glow as a documentation viewer for all users. Therefore it is better UI if I can include a header here with something else that is not the name of the tool e.g. "Welcome to the docs".

If that seems doable, I can submit the PR with a config option.

[bashbunni]

Moved to a discussion in case anyone else has the same request. The related PR is #331