cloudgov to atlasgov (#25)

Author: zach-carr

source/index.txt

@@ -31,7 +31,7 @@ comparisons between |cloudgov-short| features and their commercial
 Many procedures and reference materials are identical across 
 |cloudgov-short| and commercial |service|. In those cases, this 
 documentation provides links to the |service| documentation.
-**We recommend opening Atlas links in a new browser tab to save your place in the MongoDB CloudGov documentation.**
+**We recommend opening Atlas links in a new browser tab to save your place in the MongoDB AtlasGov documentation.**
 
 Links to the |service| documentation are presented: