Update nitro-rpc-client installation steps

testnet-onboarding-demo.md

@@ -331,19 +331,21 @@
     ```bash
     cd tls
     make create-cert
+
+    # Go back to go-nitro
+    cd ../
     ```
 
-4. Install `nitro-rpc-client` package globally (run outside of go-nitro):
+4. Install `nitro-rpc-client` package globally:
 
     ```bash
-    cd ~
-    # 'yarn global' commands only work with Yarn versions below 2.x.
+    # In go-nitro
+    npm install -g ./packages/nitro-rpc-client
 
-    npm install -g <go-nitro-repo-absolute-path>/packages/nitro-rpc-client
+    # Confirm global installation by running
+    nitro-rpc-client --version
     ```
 
-    - Replace `<go-nitro-repo-absolute-path>` with absolute path to the cloned go-nitro repo
-
 ## Run
 
 - Start L1, L2 stacks: