Update README.md

Author: sc0Vu

README.md

@@ -1,3 +1,71 @@
 # js-secp256k1
 [![Build Status](https://travis-ci.org/sc0Vu/js-secp256k1.svg?branch=master)](https://travis-ci.org/sc0Vu/js-secp256k1)
+[![codecov](https://codecov.io/gh/sc0Vu/js-secp256k1/branch/master/graph/badge.svg)](https://codecov.io/gh/sc0Vu/js-secp256k1)
+
 Compiled webassembly of bitcoin secp256k1
+
+# Install
+
+* install library
+
+```BASH
+$ npm install js-secp256k1
+```
+
+# Build with emscripten
+
+You can build secp256k1 wasm yourself with emscripten. We build two version of secp256k1 - node and web. The only difference is that there is no file system in web version.
+
+```BASH
+$ sh build.sh
+```
+
+After build wasm files, you should build javascript library again.
+
+```BASH
+$ npm run build
+```
+
+# Usage
+
+* Hash message
+```JS
+// for nodejs
+const secp256k1Async = require('js-secp256k1/dist/node-bundle')
+// or
+const secp256k1Async = require('js-secp256k1').node
+
+// for browser
+const secp256k1Async = require('js-secp256k1/dist/browser-bundle')
+// or
+const secp256k1Async = require('js-secp256k1').browser
+
+// initialize the library
+secp256k1 = await secp256k1Async()
+
+// generate public key from private key
+const privKey = Buffer.from([......])
+let pubkey = secp256k1.privkeyToPubkey(privkey)
+
+// serialize public key
+let compressed = true
+let cpubkey = secp256k1.serializePubkey(pubkey, compressed)
+
+// sign
+// signature {
+//   signature: <Buffer/Uint8Array>,
+//   recovery: <int>
+// }
+let sig = secp256k1.sign(msg, privkey)
+
+// verify
+let isVerified secp256k1.verify(msg, sig.signature, pubkey)
+
+// recover
+let rpubkey = secp256k1.recover(msg, sig.signature, sig.recovery)
+```
+
+# License
+
+MIT
+