docs: improve formatting, grammar, and links in CONTRIBUTING.md

- 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"
- "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 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

CONTRIBUTING.md

@@ -2,30 +2,31 @@
 
 ## Reporting bugs
 
-Report any bugs on github: <https://github.com/ezolenko/rollup-plugin-typescript2/issues>.
+Report any bugs [in the GitHub Issue Tracker](https://github.com/ezolenko/rollup-plugin-typescript2/issues).
 
-Attach your `tsconfig.json`, `package.json` (for versions of dependencies), rollup script and anything else that could influence module resolution, ambient types and typescript compilation.
+Attach your `tsconfig.json`, `package.json` (for versions of dependencies), `rollup.config.js`, and anything else that could influence module resolution, ambient types, and TS compilation.
 
-Check if problem is reproducible after running `npm prune` to clear any rogue types from npm_modules (by default typescript grabs all ambient types).
+Check if the problem is reproducible after running `npm prune` to clear any rogue types from `node_modules` (by default TS grabs _all_ ambient types).
 
-Check if you get the same problem with `clean` option set to true (might indicate a bug in the cache).
+Check if you get the same problem with `clean` option set to `true` (might indicate a bug in the cache).
 
-If makes sense, check if running `tsc` directly produces similar results.
+If it makes sense, check if running `tsc` directly produces similar results.
 
 Attach plugin output with `verbosity` option set to 3 (this will list all files being transpiled and their imports).
 
 ## Developing
 
-Use the normal github process of forking, making a branch and creating a PR when ready. Fix all linting problems (run `npm lint`), fix any failed checks that are run on the PR (basically lint right now). Use an editor that supports editorconfig, or match the settings from `.editorconfig` file manually.
+Use the [standard GitHub process](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/getting-started/about-collaborative-development-models#fork-and-pull-model) of forking, making a branch, and creating a PR when ready. Fix all linting problems (`npm run lint`) and fix any failed checks on the PR. Use an editor that supports `editorconfig`, or match the settings from [`.editorconfig`](./.editorconfig) manually.
 
-Fastest way to test changes is to do a self build, the plugin is part of its own build system:
-- make changes
-- run `npm build` (uses last released version on npm)
-- check that you get expected changes in `dist`
-- run `npm build-self` (uses fresh local build)
-- check `dist` for the expected changes
-- run `npm build-self` _again_ to make sure plugin built by new version can still build itself
+Fastest way to test changes is to do a self build; the plugin is part of its own build system:
 
-If `build-self` breaks at some point, fix the problem and restart from `build` step (a known good copy).
+1. make changes
+1. run `npm build` (uses last released version on npm)
+1. check that you get expected changes in `dist`
+1. run `npm build-self` (uses fresh local build)
+1. check `dist` for the expected changes
+1. run `npm build-self` _again_ to make sure plugin built by new version can still build itself
 
-This repo badly needs unittests and integration tests with various scenarios and expected outcomes though.
+If `build-self` breaks at some point, fix the problem and restart from the `build` step (a known good copy).
+
+This repo badly needs unit tests and integration tests with various scenarios and expected outcomes though.