Sidepanel example

[FlavioZanoni]

Hello, I was using the template and needed to use it with the browser sidepanel, but there was no doc and no build step for the sidepanel, so i`ve made the necessary changes in this fork

I did not test it in Firefox due to an issue where it says that I can`t upload due to the ext being MV3.
Are the firefox builds currently working ?

I can open a PR with the changes if you see that it has any value for the project

[brauliobo]

thanks for sharing @FlavioZanoni, I'll give it a try with @pvfm