Manual plugin install instructions are missing

[gonX]

This can be relevant for users which have internet issues, or for some other reason have a plugin manager that isn't working correctly.

The gist is:

• Make Plugins folder in OTD's appdata
• Make dedicated folder for the plugin - same name as the zip is suggested
• Put all relevant dll files into the folder

Example final application directory structure:

/OTD-appdata/settings.json
/OTD-appdata/Plugins/MyPlugin/MyPlugin.dll
/OTD-appdata/Plugins/MyPlugin/SomeDependency.dll

The appdata location is documented at https://opentabletdriver.net/Wiki/FAQ/General#appdata