Update README with number information

See stleary#162

Author: stleary

README

@@ -63,6 +63,11 @@ XMLTokener.java: XMLTokener extends JSONTokener for parsing XML text.
 
 Unit tests are maintained in a separate project. Contributing developers can test JSON-java pull requests with the code in this project: https://github.com/stleary/JSON-Java-unit-test
 
+Numeric types in this package comply with ECMA-404: The JSON Data Interchange Format (http://www.ecma-international.org/p
+ublications/files/ECMA-ST/ECMA-404.pdf) and RFC 7159: The JavaScript Object Notation (JSON) Data Interchange Format (https:/
+/tools.ietf.org/html/rfc7159#section-6). This package fully supports Integer, Long, and Double Java types. Partial support for BigInteger and BigDecimal values in JSONObject and JSONArray objects is pr
+ovided in the form of get(), opt(), and put() API methods.
+
 Release history:
 
 20151123    JSONObject and JSONArray initialization with generics. Contains the