Update README

The new readme reflects the new purpose of sp-client: to be a
silent payments library operating on the level of a wallet.

README.md

@@ -1,23 +1,7 @@
-# SP backend
+# SP client
 
-This is the silent payments backend for our flutter silent payments wallet [Donationwallet](https://github.com/cygnet3/donationwallet).
+Sp-client is a library that can be used to build silent payment wallets.
+It builds on top of [rust-silentpayments](https://github.com/cygnet3/rust-silentpayments).
 
-Our wallet uses nakamoto (a BIP158 client) and rust-silentpayments. To communicate with flutter, we use flutter\_rust\_bridge.
-
-## Generate binaries for android
-
-Generating the binaries for android requires installing `cargo-ndk`. Install it by running `cargo install cargo-ndk`. You may also need to add your desired toolchains:
-
-```
-rustup target add \
-    aarch64-linux-android \
-    armv7-linux-androideabi \
-    x86_64-linux-android \
-    i686-linux-android
-```
-
-After these are installed, run `just build-android` (or just copy the command found in the `justfile`).
-
-## Updating flutter api
-
-To bridge between flutter and rust, the interface in `src/api.rs` is exposed to flutter. Whenever this file is updated, you need to run `flutter_rust_bridge_codegen`. First install it using `cargo install flutter_rust_bridge_codegen`, then run `just gen` (or copy the command found in the `justfile`.
+Whereas rust-silentpayments concerns itself with cryptography (it is essentially a wrapper around secp256k1 for some silent payments logic),
+sp-client is concerned with high-level wallet stuff, such as parsing incoming transactions, managing owned outputs, and signing transactions.