Add git one-liner to find number of commits per subfolder

Also add a subfolder to store similar small git tricks

Author: JKrag

small-git-tricks/commits-per-subfolder.md

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+# Find number of commits per subfolder
+
+Just wanted to share a oneliner I whipped up, for that use case where you want to analyse a big git repo 
+and find out in which folder the activity has been. 
+I.e. If you are considering splitting up a repo with a couple 100k commits, then it can be good  to estimate 
+the number of commits in the subfolders being split out.
+
+`for dir in ./*; do (echo "$dir " && git rev-list --count HEAD --  "$dir"); done`
+
+Yes, this also includes any direct files in root folder, but I didn’t bother excluding those. 
+Feel free to improve and share back.