Add link to extensions tutorial (#19)

Author: rly

_pages/home.md

@@ -10,7 +10,7 @@ permalink: /
 
 The [Neurodata Extensions Catalog (NDX Catalog)](https://github.com/nwb-extensions) is a community-led catalog of extensions to the [Neurodata Without Borders (NWB)](https://neurodatawithoutborders.github.io/) data standard.
 
-To add an extension to this Catalog, please follow the [instructions in the staged-extensions repo](https://github.com/nwb-extensions/staged-extensions).
+To create an NWB extension, please follow [this tutorial](https://nwb-overview.readthedocs.io/en/latest/extensions_tutorial/extensions_tutorial_home.html). To add an extension to this Catalog, follow the [instructions in the staged-extensions repo](https://github.com/nwb-extensions/staged-extensions).
 
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