Add instructions on how to update extension

[manuelfcreis]

Summary

• Adds a simple explanation on how to update this extension. I noticed an update but wasn't sure on how to actually do update the extension as this is the only gh extension I use.

• I tried to follow the style in the rest of the markdown.

• Feel free to close if you feel it isn't relevant to add this here!

Thanks for the great extension by the way! 🥂

[dlvhdr]

Thanks for the contrib!