add comment explaining why "versions: <1" should be ignored

Author: djeebus

.github/dependabot.yml

@@ -7,6 +7,8 @@ updates:
           - "minor"
           - "patch"
     ignore:
+      # projects that aren't at 1.0 yet tend to have breaking changes,
+      # so we don't batch those up with this "stable small changes" group
       versions: "<1"
     package-ecosystem: "gomod"
     schedule: