Rider has no "Project Structure", how to see all excluded Directories?

Show all files is under cog menu in solution explorer.

For anyone else googling.  No one seems to have the right answer on how to include a file back into the project after you accidentally excluded it.
This is how you un-exclude, or re-include the directory or file back into your project.

You may be in a Unity view because you're working with Rider and Unity. 

• Switch to the Solution View
• 
• Right Click on Assets and choose Add -> Existing Item...
• 
• Select the folder or file you accidentally excluded
• Repeat for any others
• Now everything should work correctly again