add ipynb extension

Author: odhondt

mkdocs.yml

@@ -7,7 +7,7 @@ nav:
     - Example 1: s1-discover-insar-pairs.ipynb
     - Example 2: s1-easy-tops-insar.ipynb
     - Example 3: s1-easy-slc-geocoding.ipynb
-    - Example 4: s1-easy-terrain-flattening
+    - Example 4: s1-easy-terrain-flattening.ipynb
     - Example 5: s1-custom-pipeline.ipynb
     - Example 6: s1-goldstein-phase-denoising.ipynb
     - Example 7: discover-and-process-s2.ipynb