Restore --check option docs (#5674)

docs/api.md

@@ -18,7 +18,7 @@ prettier.format("foo ( );", { semi: false, parser: "babylon" });
 
 ## `prettier.check(source [, options])`
 
-`check` checks to see if the file has been formatted with Prettier given those options and returns a `Boolean`. This is similar to the `--list-different` parameter in the CLI and is useful for running Prettier in CI scenarios.
+`check` checks to see if the file has been formatted with Prettier given those options and returns a `Boolean`. This is similar to the `--check` or `--list-different` parameter in the CLI and is useful for running Prettier in CI scenarios.
 
 ## `prettier.formatWithCursor(source [, options])`
 

docs/cli.md

@@ -21,6 +21,38 @@ Don't forget the quotes around the globs! The quotes make sure that Prettier exp
 
 Prettier CLI will ignore files located in `node_modules` directory. To opt-out from this behavior use `--with-node-modules` flag.
 
+## `--check`
+
+When you want to check if your files are formatted, you can run Prettier with the `--check` flag (or `-c`).
+This will output a human-friendly message and a list of unformatted files, if any.
+
+```bash
+prettier --check "src/**/*.js"
+```
+
+Console output if all files are formatted:
+
+```
+Checking formatting...
+All matched files use Prettier code style!
+```
+
+Console output if some of the files require re-formatting:
+
+```
+Checking formatting...
+src/fileA.js
+src/fileB.js
+Code style issues found in the above file(s). Forgot to run Prettier?
+```
+
+The command will return exit code 1 in the second case, which is helpful inside the CI pipelines.
+Human-friendly status messages help project contributors react on possible problems.
+To minimise the number of times `prettier --check` finds unformatted files, you may be interested in configuring a [pre-commit hook](precommit.md) in your repo.
+Applying this practice will minimise the number of times the CI fails because of code formatting problems.
+
+If you need to pipe the list of unformatted files to another command, you can use [`--list-different`](./cli.md#list-different) flag instead of `--check`.
+
 ## `--debug-check`
 
 If you're worried that Prettier will change the correctness of your code, add `--debug-check` to the command. This will cause Prettier to print an error message if it detects that code correctness might have changed. Note that `--write` cannot be used with `--debug-check`.
@@ -72,6 +104,8 @@ Another useful flag is `--list-different` (or `-l`) which prints the filenames o
 prettier --single-quote --list-different "src/**/*.js"
 ```
 
+You can also use [`--check`](./cli.md#check) flag, which works the same way as `--list-different`, but also prints a human-friendly summary message to stdout.
+
 ## `--no-config`
 
 Do not look for a configuration file. The default settings will be used.

docs/options.md

@@ -310,7 +310,7 @@ If you want to make sure that your git repository only contains Linux-style line
 
 1. Set `endOfLine` option to `lf`
 1. Configure [a pre-commit hook](./precommit.md) that will run Prettier
-1. Configure Prettier to run in your CI pipeline (e.g. using [`prettier-check` npm package](https://www.npmjs.com/package/prettier-check))
+1. Configure Prettier to run in your CI pipeline using [`--check` flag](./cli.md#check)
 1. Ask Windows users to run `git config core.autocrlf false` before working on your repo so that git did not convert `LF` to `CRLF` on checkout.
    Alternatively, you can add `* text=auto eol=lf` to the repo's `.gitattributes` file to achieve this.