[doc] List features on README

README.md

-dup-crypto-rs
+# DUP Crypto
+
+Cryptographic toolkit for the DUBP(1) and DUNP(2) protocols.
+
+(1): DUniter Blockchain Protocol  
+(2): DUniter Network Protocol
+
+## Features
+
+* Rust traits to implement to any entity that can be signed.
+* Base 16/58/64 encoding/decoding
+* Sha256 hash function
+* Secure random byte generation
+* Scrypt to generate seed from credentials.
+* Ed25519 functions to create and use ed25519 keypair.