Clarify the contributing guidelines for the main list versus MORE.md

[Rangi42]

Fixes #262

Currently the guidelines link to issue #96 for "discussion" of the criteria for adding a resource to the "Awesome" list. I think this could be more helpful -- issue discussion is inherently premature, with potentially conflicting viewpoints being hashed out, and not being part of the actual document implies that it's not essential to read.

Meanwhile, the criteria actually listed in CONTRIBUTING.md don't quite clarify why a project wouldn't "deserve" to be on the Awesome List, despite meeting the (lenient) criteria we list. A "minimal working state", "minimal documentation", "something interesting" -- most people's projects already meet that qualification.

Of course, the issue #96 discussed this exact tension, between this list as a curated set of widely-useful resources, versus being "a raw list of everything related to Game Boy (Development) in general". If we want MORE.md to be for the latter, I think that should be stated explicitly, so I opened this PR to do it.

(As it currently stands, it sounds like MORE.md is for incomplete, buggy, abandoned work -- which as far as I know is not the intention. It's not a dumping grounds for work not even good enough to be on the main list. It's a place for work which fails some essential criterion of the main list, but makes up for it in other ways, e.g. a high-quality popular tutorial that happens not to be in English, or a half-finished demo that still shows off some unique trick.)

I borrowed some of the phrasing here from people discussion in that issue. Maybe more of it should be here. Before reading over its comments, I had inferred that the "awesome" list is for widely useful, technically interesting, historically relevant, or already popular links. Maybe those really are our general criteria, so we could spell them out here. But ISSOtm actually critiqued "historically important" in that issue: "From a preservation standpoint, yes; from a usability standpoint, not if it has been improved." So maybe we should explicitly state that historic but supserseded resources belong in MORE.md. (And review what's currently on the list since some of it maybe ought to be moved there by now.)