By default only the files/folders in the user's ~/workspace directory can be viewed in the directory sidebar and opened in the IDE. There are two ways to see files that are outside of the home directory in the directory sidebar.
The first option is to use hard links to the files. A hard link can be created as follows:
ln /home/nt-user/.profile /home/nt-user/workspace/.profile
This will allow the .profile file to be viewed in the directory sidebar and opened/edited in the editor.
Alternatively, if there are many files or folders in another directory that you want to make visible in the directory sidebar, you can change the default directory for the project. In the image below the default directory was updated from /home/nt-user/workspace to /home/nt-user.