git-sizer: add page (#2021)

pages/common/git-sizer.md

@@ -0,0 +1,15 @@
+# git sizer
+
+> Computes various Git repository size metrics and alerts you to any that might cause problems or inconvenience.
+
+- Report only statistics that have a level of concern greater than 0:
+
+`git sizer`
+
+- Report all statistics:
+
+`git sizer -v`
+
+- See additional options:
+
+`git sizer -h`