Backport PR #13267: Document that `%run` can execute notebooks and ipy scripts.

IPython/core/magics/execution.py

@@ -532,7 +532,18 b' python-profiler package from non-free.""")'
         
           %run [-n -i -e -G]
                [( -t [-N<N>] | -d [-b<N>] | -p [profile options] )]
-               ( -m mod | file ) [args]
+               ( -m mod | filename ) [args]
+
+        The filename argument should be either a pure Python script (with
+        extension ``.py``), or a file with custom IPython syntax (such as
+        magics). If the latter, the file can be either a script with ``.ipy``
+        extension, or a Jupyter notebook with ``.ipynb`` extension. When running
+        a Jupyter notebook, the output from print statements and other
+        displayed objects will appear in the terminal (even matplotlib figures
+        will open, if a terminal-compliant backend is being used). Note that,
+        at the system command line, the ``jupyter run`` command offers similar
+        functionality for executing notebooks (albeit currently with some
+        differences in supported options).
 
         Parameters after the filename are passed as command-line arguments to
         the program (put in sys.argv). Then, control returns to IPython's