Build: Correct LICENSE paths for wheels and document the bundled Cython runtime

LICENSE

@@ -216,7 +216,9 @@ License: https://www.apache.org/licenses/LICENSE-2.0
 
 This product includes code from Apache Thrift.
 
-* Uses the fb303.thrift file that's part of Hive's thrift service in vendor/fb303/
+* Includes the generated Python client and type definitions for the fb303
+  service. In source distributions, this code is located in vendor/fb303/; in
+  binary distributions, it is shipped as the top-level fb303 package.
 
 Copyright: 2006-2022 The Apache Software Foundation.
 Home page: https://thrift.apache.org/
@@ -226,10 +228,25 @@ License: https://www.apache.org/licenses/LICENSE-2.0
 
 This product includes code from Apache Hive.
 
-* Uses hive_metastore.thrift to generate the Hive Metastore client in vendor/hive_metastore/
+* Includes the Hive Metastore client generated from hive_metastore.thrift. The
+  generated code is located in vendor/hive_metastore/ in source distributions
+  and shipped as the top-level hive_metastore package in binary distributions.
 
 Copyright: 2008-2022 The Apache Software Foundation.
 Home page: https://hive.apache.org/
 License: https://www.apache.org/licenses/LICENSE-2.0
 
 --------------------------------------------------------------------------------
+
+Official binary distributions contain the pyiceberg.avro.decoder_fast
+extension, built from C code generated by Cython.
+
+* Cython generates this C code from pyiceberg/avro/decoder_fast.pyx. Cython
+  states that compilation may embed snippets in generated output, but that the
+  output is not a derivative work of Cython and those snippets impose no
+  license restrictions.
+
+Cython licensing clarification:
+https://github.com/cython/cython/blob/2f3a781dcca092ce95fbfef2736b12b0d1ab50dd/COPYING.txt
+
+--------------------------------------------------------------------------------