You can edit your code with an editor started externally from the IDE (e.g. from the command line). When you're done editing, you'll have to synchronize the IDE with the changes.
To synchronize the IDE with the changes you've made using an external editor outside of the IDE, in the Project Explorer view, right-click the tree pane and select Refresh. The IDE is updated to reflect any changes you've made (such as creating new files or re-indexing changed files).