Consider making the Requesting New Types information more visible

[alrra]

Most of the recent pull requests contained commits that tried to change the mime.types file instead of node.types.

I suspect this is because the majority of people don't read wikis and few ever read the README.md carefully (thus not seeing / following the "requesting new types" link to the wiki).

So, I think it would be better to just move the information from the wiki somewhere where it can be immediately visible, like, for example, in the README.md or maybe into a CONTRIBUTING.md file.

[broofa]

node-mime now sits on top of https://github.com/jshttp/mime-db. (i.e. this project is no longer in the business of managing custom mime extensions.)