adding readme

Author: george-larionov

contrib/bech32/README.md

@@ -0,0 +1,9 @@
+Code copied from the [bech32](https://github.com/sipa/bech32) repository. It contains reference implementations 
+of the Bech32 and Bech32m algorithms, along with an implementation of the SegWit algorithm which is a 
+specialization of Bech32(m) for Bitcoin. The code used in ClickHouse is only the Bech32 algorithms, not SegWit. 
+See [this link](https://en.bitcoin.it/wiki/Bech32) for more info on the algorithms and their applications.
+
+Modifications to the code:
+- typedef changed to using as per compiler warnings
+- Problematic asserts were changed to if statement + empty return
+- convertbits function was copied directly into src/Functions/FunctionsBech32Representation.cpp