add zero-import get_ipython example

docs/source/whatsnew/version1.0.txt

@@ -70,7 +70,17 b' We also have added:'
 Which is a *library* function for getting the current IPython instance,
 and will return ``None`` if no IPython instance is running.
 This is the official way to check whether your code is called from inside an IPython session.
+If you want to check for IPython without unnecessarily importing IPython,
+use this function:
 
+.. sourcecode:: python
+
+    def get_ipython():
+        """return IPython instance if there is one, None otherwise"""
+        import sys
+        if "IPython" in sys.modules:
+            import IPython
+            return IPython.get_ipython()
 
 Core
 ----