upgrade Readme.md

Author: RCasatta

Readme.md

@@ -11,10 +11,40 @@ let bitcoind = bitcoind::BitcoinD::new("/usr/local/bin/bitcoind").unwrap();
 assert_eq!(0, bitcoind.client.get_blockchain_info().unwrap().blocks);
 ```
 
+## Automatic binaries download
+
+When a feature like `22_0` is selected, the build script will automatically download the bitcoin core version `22.0`, verify the hashes and place it in the build directory for this crate.
+Use utility function `downloaded_exe_path()` to get the downloaded executable path.
+
+### Example 
+
+In your project Cargo.toml, activate the following features
+
+```toml
+
+[dev-dependencies]
+bitcoind = { version = "0.20.0", features = "22_0" }
+```
+
+Then use it:
+
+```rust
+let bitcoind = bitcoind::BitcoinD::new(bitcoind::downloaded_exe_path().unwrap()).unwrap();
+```
+
 ## MSRV
 
 1.41.1
 
+## Issues with traditional approach
+
+I used integration testing based on external bash script launching needed external processes, there are many issues with this approach like:
+
+* External script may interfere with local development environment https://github.com/rust-bitcoin/rust-bitcoincore-rpc/blob/200fc8247c1896709a673b82a89ca0da5e7aa2ce/integration_test/run.sh#L9
+* Use of a single huge test to test everything https://github.com/rust-bitcoin/rust-bitcoincore-rpc/blob/200fc8247c1896709a673b82a89ca0da5e7aa2ce/integration_test/src/main.rs#L122-L203
+* If test are separated, a failing test may fail to leave a clean situation, causing other test to fail (because of the initial situation, not a real failure)
+* bash script are hard, especially support different OS and versions
+
 ## Features
 
   * It waits until bitcoind daemon become ready to accept RPC commands
@@ -23,25 +53,19 @@ assert_eq!(0, bitcoind.client.get_blockchain_info().unwrap().blocks);
   * the process is killed when the struct goes out of scope no matter how the test finishes
   * allows easy spawning of dependent process like https://github.com/RCasatta/electrsd
 
-## Cargo features
+Thanks to these features every `#[test]` could easily run isolated with its own environment.
 
-When a feature like `0_21_1` is selected, the build script will automatically download the bitcoin core version 0.21.1
-and verify the hashes and place it in the build directory for this crate.
-Use utility function `downloaded_exe_path()` to get the downloaded executable path.
+## Used by
 
-### Example
+* [firma](https://github.com/RCasatta/firma/)
+* [payjoin](https://github.com/Kixunil/payjoin)
 
-##### Cargo.toml
+### Via bdk dependency
 
-```toml
+* [gun](https://github.com/LLFourn/gun)
 
-[dev-dependencies]
-bitcoind = { version = "0.12.0", features = "0_21_1" }
-```
-
-#### In your tests
-
-```rust
-let bitcoind = bitcoind::BitcoinD::new(bitcoind::downloaded_exe_path().unwrap()).unwrap();
-```
+### Via electrsd dependency:
 
+* [bdk](https://github.com/bitcoindevkit/bdk)
+* [BEWallet](https://github.com/LeoComandini/BEWallet)
+* [gdk rust](https://github.com/Blockstream/gdk/blob/master/subprojects/gdk_rust/)