Remove the byte order mark from the Czech Javascript file. This file… (#2509)

* Remove the byte order mark from the Czech Javascript file.  This file wasn't showing up on the site before but this will fix it :)

* Add info on how to check if a file has a byte order marker to the CONTRIBUTING file

* Fit into 80 columns width

CONTRIBUTING.markdown

@@ -33,6 +33,9 @@ review them more effectively and/or individually.
     your file is UTF-8 encoded.
   + Try to leave out the byte-order-mark at the start of the file. (`:set nobomb`
     in Vim)
+  + You can check if the file contains a BOM on Linux/Unix systems by running
+    `file language.html.markdown`  You will see this if it uses a BOM:
+	`UTF-8 Unicode (with BOM) text`.
 
 
 ### Header configuration

cs-cz/javascript.html.markdown

@@ -1,4 +1,4 @@
----
+---
 language: javascript
 contributors:
     - ["Adam Brenecki", "http://adam.brenecki.id.au"]