update docs

Author: RetricSu

docs/migration.md

@@ -1,3 +1,25 @@
+# Migration from v0.3.x to v0.4.x
+
+## BREAKING CHANGES
+
+1. The default log level in devnet is changed to `warn,ckb-script=debug` from `info`
+2. The devnet RPC proxy sever is now default running, and proxy port is changed to `28114` from `9000`
+3. The `create` command is now focusing on creating a CKB Smart Contract project in JavaScript, instead of a dApp project.
+4. `offckb.config.ts` file is removed, and the `deploy` command now requires `--target` and `--output` options to specify the contract binary file or folder path and the output folder path.
+5. `ckb-js-vm` is now added to built-in scripts in offckb devnet.
+6. `system-scripts` command has a new option called `-o, --output` to specify the output json file path for the system scripts.
+7. The build system is changed from `npm-shrinkwrap.json` to `ncc` toolchain.
+
+## Removed commands
+
+- `proxy-rpc`
+- `mol`
+- `repl`
+- `list-hashes`
+- `my-scripts`
+- `sync-scripts`
+- `inject-config`
+
 # Migration from v0.2.x to v0.3.x
 
 ## BREAKING CHANGES