README: Clarify ignoreUnimportedSymbols works for unused imports

Author: sirbrillig

README.md

@@ -106,6 +106,8 @@ You can ignore certain patterns by using the `ignoreUnimportedSymbols` config op
 </ruleset>
 ```
 
+Despite the name, you can also use the `ignoreUnimportedSymbols` pattern to ignore specific unused imports.
+
 ## Usage
 
 Most editors have a phpcs plugin available, but you can also run phpcs manually. To run phpcs on a file in your project, just use the command-line as follows (the `-s` causes the sniff code to be shown, which is very important for learning about an error).