Merge pull request #19 from nsidc/update-index-dat-pages

Update index with reference to DAT backend docs pages

Author: trey-stafford

index.md

@@ -8,3 +8,9 @@ Welcome to the NSIDC [GitHub Pages](https://pages.github.com/) home page. This s
   to searching, accessing and working with NSIDC data.
 * [NSIDC Technical Blog](https://nsidc.github.io/NSIDC-Technical-Blog/): A blog
   by and for NSIDC developers.
+* [NASA NSIDC DAAC Data Access Tool (DAT) backend
+  documentation](https://nsidc.github.io/data-access-tool-backend/):
+  documentation for the backend services powering the web-based [Data Access
+  Tool UI](https://github.com/nsidc/data-access-tool-ui), which serves as an
+  interface for users to find, filter, and download data files associated with
+  NSIDC DAAC datasets.