Here’s how to add “Open in Terminal” in the context menu (right-click menu) of folders in Finder:

Go to System Preferences→Keyboard→Keyboard Shortcuts→Services and enable “New Terminal at Folder” (or “New Terminal tab at Folder”). It is also possible to add a keyboard shortcut for the command, e.g. Shift-Command-T. Adding a shortcut will disable the service from the context menu list so you might want to enable it again by checking the box.