Does anyone know if there is documentation about updating the sidebar on MyAccount to include a new entry?

Have a look at this: https://system.netsuite.com/help/helpcenter/en_US/APIs/SuiteCommerce/Extensibility/Frontend/MyAccountMenu.html

Thanks for this Viraj. I've created my groupEntry, but I'm still unable to view it locally. Am I missing something in the initialize function of my view? Appreciate the help

You can check for a few things: 1. Was your extension/extension module created for the my account section of SC? You can check this in the manifest under "javascript.entry points" and "javascript.application". You should have entries for my account. If not, you may have to add them for your files accordingly. 2. Is your entry JS being called and is the Extensibility API method being triggered? These 2 are the first things that come to my mind that you can check.