Update README and RELEASE for new S3 support

Author: Patrick O'Brien

README.rst

@@ -90,6 +90,7 @@ Optional dependencies
      * openpyxl version 1.6.1 or higher, for writing .xlsx files
      * xlrd >= 0.9.0
      * Needed for Excel I/O
+  * `boto <https://pypi.python.org/pypi/boto>`__: necessary for Amazon S3 access.
 
 
 Installation from sources

RELEASE.rst

@@ -32,6 +32,7 @@ pandas 0.11.1
 
   - pd.read_html() can now parse HTML string, files or urls and return dataframes
     courtesy of @cpcloud. (GH3477_)
+  - Support for reading Amazon S3 files. (GH3504_)
 
 **Improvements to existing features**