Update readme

Author: methane

README.md

@@ -15,15 +15,10 @@ This package provides CPython bindings for reading and writing MessagePack data.
 
 ### PyPI package name
 
-TL;DR: When upgrading from msgpack-0.4 or earlier, don't do `pip install -U msgpack-python`.
-Do `pip uninstall msgpack-python; pip install -U msgpack` instead.
+Package name on PyPI was changed from `msgpack-python` to `msgpack` from 0.5.
 
-Package name on PyPI was changed to msgpack from 0.5.
-I upload transitional package (msgpack-python 0.5 which depending on msgpack)
-for smooth transition from msgpack-python to msgpack.
-
-Sadly, this doesn't work for upgrade install.  After `pip install -U msgpack-python`,
-msgpack is removed, and `import msgpack` fail.
+When upgrading from msgpack-0.4 or earlier, do `pip uninstall msgpack-python` before
+`pip install -U msgpack`.
 
 
 ### Compatibility with the old format