docs: README, contributor guidelines (#466)

* contributor guidelines

* notes

* README

README.md

@@ -7,6 +7,8 @@ parent:
   <h1> Ethermint </h1>
 </div>
 
+![banner](docs/ethermint.jpg)
+
 <div align="center">
   <a href="https://github.com/tharsis/ethermint/releases/latest">
     <img alt="Version" src="https://img.shields.io/github/tag/tharsis/ethermint.svg" />
@@ -42,9 +44,7 @@ parent:
 Ethermint is a scalable, high-throughput Proof-of-Stake blockchain that is fully compatible and
 interoperable with Ethereum. It's build using the the [Cosmos SDK](https://github.com/cosmos/cosmos-sdk/) which runs on top of [Tendermint Core](https://github.com/tendermint/tendermint) consensus engine.
 
-> **WARNING:** Ethermint is under VERY ACTIVE DEVELOPMENT and should be treated as pre-alpha software. This means it is not meant to be run in production, its APIs are subject to change without warning and should not be relied upon, and it should not be used to hold any value. We will remove this warning when we have a release that is stable, secure, and properly tested.
-
-**Note**: Requires [Go 1.15+](https://golang.org/dl/)
+**Note**: Requires [Go 1.16+](https://golang.org/dl/)
 
 ## Quick Start