Update readme

Author: kronolynx

README.md

@@ -4,4 +4,30 @@
 This is an implementation of [Lightning BOLT11 Specification](https://github.com/lightningnetwork/lightning-rfc/blob/master/11-payment-encoding.md) for providing a minimal QR-code-ready format for requesting
 lightning payments.
 
-## WIP
+## Usage
+
+Add this to your `Cargo.toml`:
+
+```toml
+[dependencies]
+bolt11 = "0.1.0"
+```
+
+and this to your crate root:
+
+```rust
+extern crate bolt11;
+```
+
+## Example
+
+```rust
+use bolt11::payment_request::PaymentRequest;
+
+let encoded_payment_request = "lnbc2500u1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqf
+    qqqsyqcyq5rqwzqfqypqdq5xysxxatsyp3k7enxv4jsxqzpuaztrnwngzn3kdzw5hydlzf03qdgm2hdq
+    27cqv3agm2awhz5se903vruatfhq77w3ls4evs3ch9zw97j25emudupq63nyw24cg27h2rspfj9srp";
+
+let payment_request = PaymentRequest::decode(encoded_payment_request);
+
+```