Added customizable RTC tutorial (#306)

* Added customizable RTC tutorial

Author: Tom Augspurger

docs/index.md

@@ -39,6 +39,7 @@ quickstarts/storage
 :caption: Tutorials
 
 tutorials/cloudless-mosaic-sentinel2
+Sentinel-1 Customizable Radiometric Terrain Correction <tutorials/customizable-rtc-sentinel1>
 tutorials/landcover
 tutorials/hurricane-florence-animation
 See all tutorials <https://github.com/microsoft/PlanetaryComputerExamples/tree/main/tutorials>

etl/config/external_docs_config.yml

@@ -10,6 +10,7 @@
 #     - tutorials/images/another.png
 ---
 - file_url: tutorials/cloudless-mosaic-sentinel2.ipynb
+- file_url: tutorials/customizable-rtc-sentinel1.ipynb
 - file_url: tutorials/landcover.ipynb
 - file_url: tutorials/hurricane-florence-animation.ipynb
   image_urls: