Reference the existence of jsonc-mode in the README

... figured it'd save me some searching pain later

Author: offbyone

README.md

@@ -4,7 +4,7 @@ json-mode.el
 Major mode for editing JSON files.
 
 Extends the builtin js-mode to add better syntax highlighting for JSON
-and some nice editing keybindings.
+and some nice editing keybindings. 
 
 Install
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@@ -31,6 +31,11 @@ Indent Width
 
 Customize `js-indent-level`.
 
+JSON With Comments
+---
+
+In addition to JSON files, this package provides `jsonc-mode` for editing JSON with commas and comments (sometimes referred to as huJSON or JWCC).
+
 License
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