README: Use the correct argument as template parameter

v2.0.0 switched from bits to byte but this wasn't updated.

README.md

@@ -9,7 +9,7 @@ A lightweight wrapper to represent hashes as value types.
 
 ```D
 /// Alias for a 256 bits / 32 byte hash type
-alias Hash = BitBlob!256;
+alias Hash = BitBlob!32;
 
 /// Used in the following tests
 enum BTCGenesisStr = `0x000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f`;