Update docs to quote glob options (postcss#154)

Fixes postcss#142.

Author: danny-andrews

README.md

@@ -29,13 +29,13 @@ postcss [input.css] [OPTIONS] [-o|--output output.css] [-w|--watch]
 The input may also be a glob:
 
 ```bash
-postcss src/*.css [OPTIONS]
+postcss "src/*.css" [OPTIONS]
 ```
 
 Recursively read a directory:
 
 ```bash
-postcss src/**/*.css [OPTIONS]
+postcss "src/**/*.css" [OPTIONS]
 ```
 
 > ⚠️  If there are multiple input files, the --dir or --replace option must be passed.