Add links for documentation

Author: RobLoach

README.md

@@ -4,9 +4,9 @@ User contributed wrappers for ChaiScript.
 
 ## Modules
 
-- Math: Adds common math methods to ChaiScript.
-- String ID: String hashing with [string_id](https://github.com/foonathan/string_id)
-- String Methods: Introduces some extra string methods to ChaiScript strings
+- [Math](#math): Adds common math methods to ChaiScript.
+- [String ID](#string-id): String hashing with [string_id](https://github.com/foonathan/string_id)
+- [String Methods](#string-methods): Introduces some extra string methods to ChaiScript strings
 
 ### Math