Add a glob pattern as an input example (postcss#133)

Author: Zach Green

README.md

@@ -26,6 +26,18 @@ npm i -g|-D postcss-cli
 postcss [input.css] [OPTIONS] [-o|--output output.css] [-w|--watch]
 ```
 
+The input may also be a glob:
+
+```bash
+postcss src/*.css [OPTIONS]
+```
+
+Recursively read a directory:
+
+```bash
+postcss src/**/*.css [OPTIONS]
+```
+
 > ⚠️  If there are multiple input files, the --dir or --replace option must be passed.
 
 ```bash