Adds note about trusting PSGallery.

Author: kenwith

tools/office-cmdlet-updater/README.md

@@ -19,5 +19,11 @@
     - SharePoint Migration Tool (SPMT):  
 1. Run the app, type `npm start` and press Enter.
 
+## Notes
+1. The modules are installed from the PowerShell Gallery (PSGallery).
+    This gallery contains user submitted code.
+    If you would rather not install modules from the PSGallery then you can install the modules manually prior to running the tool.
+    If you need to add PSGallery as a trusted source, you can so so with the following command:
+    `Set-PSRepository -Name "PSGallery" -InstallationPolicy Trusted`
 
 ## Sample Run