- condenses the README a bit and uses the standard CONTRIBUTING.md file
  - it's a file I often look for when filing an issue or creating a PR
  - leaves the section still in the README so that users (esp. on NPM)
    will know to go there if they're not aware of that convention

- GitHub also now tells users to read the CONTRIBUTING.md of a repo when
  filing issues or creating PRs, so hopefully this helps point more
  users in the right direction as well

- slightly change reference to GH Issue Tracker

- use oxford commas everywhere for clarity
- missing "the" in a few places
- more minor grammatical fixes (missing space, semicolon vs. comma, etc)

- fix: "npm_modules" -> "`node_modules`"
- fix: "npm lint" -> "npm run lint", "npm build" -> "npm run build",
  "npm build-self" -> "npm run build-self"
  - short-hand works in Yarn and for some pre-defined Node scripts, like
    `start` and `test`, but the rest need `run`
- "typescript" -> "TS" (prefer proper "TypeScript" or just "TS")
- use backticks monospace/code formatting where appropriate

- link to GitHub's official docs on forking and making PRs
  - also use the word "standard" instead of "normal" as it's more
    inclusive and reflective that this is a convention/standard
- link to editorconfig site
- link directly to `.editorconfig` with a relative link as well
- reword portion about PR checks as they do run `build` and `build-self`
  nowadays (not sure how old this text is)

- use an ordered list (instead of unordered) for the testing process
  as this is meant to be done in order