Fix dev install steps in contributor docs (#1188)

Added CLI : `jlpm` and `jlpm build` after the install command `./scripts/install.sh`

Author: srdas

docs/source/contributors/index.md

@@ -47,6 +47,8 @@ cd <jupyter-ai-top>
 
 # Installs all the dependencies and sets up the dev environment
 ./scripts/install.sh
+jlpm
+jlpm build
 ```
 
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