docs: describe list input file to folder

Author: Scrum

readme.md

@@ -35,6 +35,7 @@ $ posthtml --help
     $ posthtml input.html
     $ posthtml input.html -o output.html
     $ posthtml inputFolder/*.html !unicorn.html
+    $ posthtml input-one.html input-two.html -o outputFolder
     $ posthtml input.html -o output.html -c posthtml.js
     $ posthtml input.html -o output.html -u posthtml-bem --posthtml-bem.elemPrefix __
     $ posthtml inputFolder/*.html -o outputFolder