chore: prettier README and add env var documentation

README.md

@@ -20,12 +20,34 @@ npm test
 
 ### Adding the language to the documentation style guide
 
-1. PR the [nodejs/node](https://github.com/nodejs/node) repo adding the language/grammar to the [documentation style guide](https://github.com/nodejs/node/blob/master/doc/guides/doc-style-guide.md)
+1. PR the [nodejs/node](https://github.com/nodejs/node) repo adding the
+   language/grammar to the
+   [documentation style guide](https://github.com/nodejs/node/blob/master/doc/guides/doc-style-guide.md).
 
 ### Adding the language to the linter
 
-1. PR this repo adding the language/grammar
-1. Bump this package version, publish it
-1. In [node-lint-md-cli-rollup](https://github.com/nodejs/node/tree/master/tools/node-lint-md-cli-rollup), bump the `remark-preset-lint-node` dependency 
-1. In the `nodejs/node` repo, rebuild the Markdown linter (`make lint-md-rollup`)
-1. PR the `nodejs/node` repo with the updated linter
+1. PR this repo adding the language/grammar.
+1. Bump this package version, publish it.
+1. In
+   [node-lint-md-cli-rollup](https://github.com/nodejs/node/tree/master/tools/node-lint-md-cli-rollup),
+   bump the `remark-preset-lint-node` dependency.
+1. In the `nodejs/node` repo, rebuild the Markdown linter
+   (`make lint-md-rollup`).
+1. PR the `nodejs/node` repo with the updated linter.
+
+## Environment variables
+
+#### `NODE_RELEASED_VERSIONS`
+
+On runtime, the linter will check the environment if the
+`NODE_RELEASED_VERSIONS` variable is defined; if it's there, it will use the
+content of the variable as a comma-separated list of allowed version numbers.
+This list is supposed to be built from the changelog(s), and validates the
+version numbers for the `nodejs-yaml-comments` rule.
+
+For better compatibility with the nodejs/node changelogs, there are a few
+exceptions:
+
+- Version numbers `^0.0.0 || ^0.1.0` are not validated using the provided list,
+  they are validating using the `vx.x.x` pattern.
+- `REPLACEME` placeholder is always valid, regardless it's in the list or not.