doc update

Author: danielaparker

README.md

@@ -28,6 +28,10 @@ jsoncons is distributed under the [Boost Software License](http://www.boost.org/
 jsoncons is free but welcomes support to sustain its development. If you find this library helpful, please consider making a [one time donation](https://paypal.me/jsoncons?locale.x=en_US)
 or becoming a [:heart: sponsor](https://github.com/sponsors/danielaparker). 
 
+As the `jsoncons` library has evolved, names have sometimes changed. To ease transition, jsoncons deprecates the 
+old names but continues to support many of them. The deprecated names can be suppressed by defining the macro 
+`JSONCONS_NO_DEPRECATED`, and this is recommended for new code.
+
 ## Extensions
 
 - [bson](doc/ref/bson/bson.md) implements decode from and encode to the [Binary JSON](http://bsonspec.org/) data format.