Add ADOPTERS file, per CNCF requirements

Signed-off-by: Matt Butcher <matt.butcher@microsoft.com>

ADOPTERS.md

@@ -0,0 +1,8 @@
+ To add your organization to this list, simply add your organization's name,
+ optionally with a link. The list is in alphabetical order.
+
+# Organizations Using Helm
+
+- [Microsoft](https://microsoft.com)
+
+_This file is part of the CNCF official documentation for projects._