Adds new intro to key management page (#181)

Author: Conor Okus

docs/key_management.md

@@ -1,10 +1,10 @@
 # Key Management
 
-Relevant reference: [Rust docs](https://docs.rs/lightning/*/lightning/chain/keysinterface/struct.KeysManager.html)
+LDK provides a simple interface that takes a 32-byte seed for use as a BIP 32 extended key and derives keys from that. Check out the [Rust docs](https://docs.rs/lightning/*/lightning/chain/keysinterface/struct.KeysManager.html)
 
 LDK Private Key Information is primarily provided through the `chain::keysinterface::KeysInterface` trait. It includes a few basic methods to get public and private key information, as well as a method to get an instance of a second trait which provides per-channel information - `chain::keysinterface::ChannelKeys`.
 
-While a custom `KeysInterface` implementation allows simple flexibility to control derivation of private keys, `ChannelKeys` focuses on signing Lightning transactions and is primarily useful if you want to store private key material on a separate device which enforces Lightning protocol details.
+While a custom `KeysInterface` implementation allows simple flexibility to control derivation of private keys, `ChannelKeys` focuses on signing lightning transactions and is primarily useful if you want to store private key material on a separate device which enforces lightning protocol details.
 
 A simple implementation of `KeysInterface` is provided in the form of `chain::keysinterface::KeysManager`, see its documentation for more details on its key derivation. It uses `chain::keysinterface::InMemoryChannelKeys` for channel signing, which is likely an appropriate signer for custom `KeysInterface` implementations as well.