Installing

There are two types of add-ins that you can install.
Production Ready - These can be centrally deployed
Developer Add-ins - These are for testing

Registry - Developer Add-in

HKCU\Software\Microsoft\Office \ 16.0 \ WEF \ Developer 

HKCU\Software\Microsoft\Office \ 16.0 \ WEF \ Developer \ "addin GUID" \ UseDirectDebugger 
HKCU\Software\Microsoft\Office \ 16.0 \ WEF \ Developer \ "addin GUID" \ UseLiveReload 
HKCU\Software\Microsoft\Office \ 16.0 \ WEF \ Developer \ "addin GUID" \ UseWebDebugger 

Registry - UseRuntimeLogging

HKCU\Software\Microsoft\Office \ 16.0 \ WEF \ Developer \ "addin GUID" \ RuntimeLogging 

add the (Default) value to your C:\Temp\LogFile.txt"

Windows Folder - Wef Subfolders

folder - C:\Users\"username"\AppData\Local\Microsoft\Office\16.0\Wef\ 

AddinInfo - aggregated info about all installed add-ins
AggregatedCache - shared cache for all add-ins
AppCommands - ribbon and app command definitions
CustomFunctions - excel custom function definitions
MetaOS - Office UI metadata and OS data
Resources - shared resources across add-ins
webview2 - webview2 runtime components (used by newer add-ins)
{GUID} - the unique GUID for an installed add-in

Add-in Package Subfolders

When an add-in is deployed using a shared folder all the resources are extracted
ExtendedManifest - extended manifest metadata
ExtendedManifestResources - resources for extended manifest
Html - the taskpane and dialog HTML files
Javascript - compiled javascript / typescript code
Manifests - the manifest.xml file
Metadata - add-in metadata
TaosAcquisition - telemetry / diagnostics data
WellKnownResources - standard resources