update readme

README.md

@@ -34,6 +34,7 @@ More relevant links:
 * [Canvas UI](https://paritytech.github.io/canvas-ui/#/upload) ‒ Frontend for contract deployment and interaction
 * [Canvas Node](https://github.com/paritytech/canvas-node) ‒ Simple Substrate blockchain which includes smart contract functionality
 
+**This is a forked version to provide debug feature in Patract's toolchain.**
 
 ## Installation
 
@@ -49,7 +50,7 @@ More relevant links:
   There's only an old version in your distributions package manager? Just use a 
   [binary release](https://github.com/WebAssembly/binaryen/releases).
 
-* Step 3: `cargo install --force cargo-contract`
+* Step 3: `cargo install --git https://github.com/patractlabs/cargo-contract.git --branch tag-v0.12.1 --force`
 
 
 ## Usage
@@ -82,6 +83,26 @@ do so is `cargo +nightly contract build`.
 To avoid having to always add `+nightly` you can also set `nightly` as the default
 toolchain of a directory by executing `rustup override set nightly` in it.
 
+###### debug feature
+
+The different of the forked from the official branch is that we have `debug` flag in command `build`.
+
+This is used for wasm backtrace, for adding `--debug` will retain the Custom/Name section part in wasm. And in debug mode,
+the default optimization for `wasm-opt` is 0, and without debug, the default optimization is 3 in original version.
+You can also set the optimization level by `--optimization-passes` in debug mode.
+
+```
+...
+
+USAGE:
+    cargo contract build [FLAGS] [OPTIONS]
+
+FLAGS:
+    -d, --debug      Enable debug info in the wasm bundle
+
+...
+```
+
 ##### `cargo contract check`
 
 Checks that the code builds as WebAssembly. This command does not output any `<name>.contract`