The Awesome project provides a couple of requirements for lists that we
should more easily make available to contributors.
Also, inform contributors of the linter.
* CONTRIBUTING.md: Request factual descriptions
In the past, we've allowed rather non-descript summary descriptions for
projects (see the `nixpkgs-hammering` entry). In order to better comply
with the official comment guidelines laid out in the parent `awesome`
project and better serve those browsing the list, update the
contributing guidelines to specify that descriptions should also be
persuasive and factual, while providing an example format.
Additionally, fix the grammar/verb-tense for the alphabetical
requirement.
* CONTRIBUTING.md: Reduce guidance for simplicity
Asking for an agile user-story is a little much... but having a
"descriptive description" is redundant, so just keep it short and
simple.
* CONTRIBUTING.md: Adjust phrasing
Rephrase the category modification guideline to match the other imperative guidelines
