Clarify eslint --print-config usage

I thought that `--print-config` to a config file path as argument, but
it takes _any_ file path as argument. ESLint starts looking for config
files from that file and upwards in the file system.

(If one wishes to specify a config file via a flag, the command is
`eslint --config config.js --print-config some/file.js`.)

README.md

@@ -58,14 +58,20 @@ First, add a script for it to package.json:
 ```json
 {
   "scripts": {
-    "eslint-check": "eslint --print-config .eslintrc.js | eslint-config-prettier-check"
+    "eslint-check": "eslint --print-config . | eslint-config-prettier-check"
   }
 }
 ```
 
 Then run `npm run eslint-check`.
 
-(Swap out .eslintrc.js with the path to your config if needed.)
+If you use [multiple configuration files] or [overrides], you may need to run
+the above script several times with different `--print-config` arguments, such
+as:
+
+```
+eslint --print-config test/index.js | eslint-config-prettier-check
+```
 
 Exit codes:
 
@@ -524,10 +530,12 @@ several other npm scripts:
 [eslint-plugin-standard]: https://github.com/xjamundx/eslint-plugin-standard
 [lines-around-comment]: https://eslint.org/docs/rules/lines-around-comment
 [max-len]: https://eslint.org/docs/rules/max-len
+[multiple configuration files]: https://eslint.org/docs/user-guide/configuring#configuration-cascading-and-hierarchy
 [no-confusing-arrow]: https://eslint.org/docs/rules/no-confusing-arrow
 [no-mixed-operators]: https://eslint.org/docs/rules/no-mixed-operators
 [no-tabs]: https://eslint.org/docs/rules/no-tabs
 [no-unexpected-multiline]: https://eslint.org/docs/rules/no-unexpected-multiline
+[overrides]: https://eslint.org/docs/user-guide/configuring#configuration-based-on-glob-patterns
 [quotes]: https://eslint.org/docs/rules/quotes
 [travis-badge]: https://travis-ci.org/prettier/eslint-config-prettier.svg?branch=master
 [travis]: https://travis-ci.org/prettier/eslint-config-prettier

bin/cli.js

@@ -16,9 +16,8 @@ if (module === require.main) {
         "This tool checks whether an ESLint configuration contains rules that are",
         "unnecessary or conflict with Prettier. It’s supposed to be run like this:",
         "",
-        "  eslint --print-config .eslintrc.js | eslint-config-prettier-check",
-        "",
-        "(Swap out .eslintrc.js with the path to your config if needed.)",
+        "  eslint --print-config . | eslint-config-prettier-check",
+        "  eslint --print-config test/index.js | eslint-config-prettier-check",
         "",
         "Exit codes:",
         "",

package.json

@@ -25,7 +25,7 @@
     "test:lint-verify-fail": "eslint test-lint/ --config .eslintrc.base.js --format json",
     "test:lint-rules": "eslint index.js --config test-config/.eslintrc.js --format json",
     "test:jest": "jest",
-    "test:cli-sanity": "eslint --print-config .eslintrc.js | node ./bin/cli.js",
+    "test:cli-sanity": "eslint --print-config . | node ./bin/cli.js",
     "test": "npm run test:lint && npm run test:jest && npm run test:cli-sanity"
   },
   "dependencies": {