update changelog

Author: timfel

CHANGELOG.md

@@ -3,6 +3,16 @@
 This changelog summarizes major changes between GraalVM versions of the Python
 language runtime. The main focus is on user-observable behavior of the engine.
 
+## Version 1.0.0 RC3
+
+* Support for more String encodings
+* Implement buffered I/O
+* Remove our random module substitute and use the standard library implementation
+* Fix a potential thread-safety problem with cached parse trees when multiple Python contexts are used from multiple threads
+* Complete support for math module builtins
+* C-API improvements to run simple scikit-learn and NumPy examples
+* Support the buffer protocol to wrap arbitrary Python sequences with no copy into NumPy arrays
+
 ## Version 1.0.0 RC2
 
 * Updates to the polyglot and embedding APIs