update readme

Author: darunrs

lazer/sdk/js/README.md

@@ -3,3 +3,15 @@
 ## Contributing & Development
 
 See [contributing.md](docs/contributing/contributing.md) for information on how to develop or contribute to this project!
+
+## Installation and build
+
+### pnpm
+
+```
+cd to crosschain root
+$ pnpm install
+$ pnpm turbo --filter @pythnetwork/pyth-lazer-sdk build
+```
+
+As part of the build, files will be generated from the proto files found in the lazer/proto folder. These generated files are placed in the src/generated/ folder.