Updated Custom Commands Compendium (markdown)

Custom-Commands-Compendium.md

@@ -2,6 +2,20 @@ If you have implemented a custom command(s) that you find useful, please add it
 
 If you want to know how to implement your own custom commands see [here](https://github.com/jesseduffield/lazygit/blob/master/docs/Custom_Command_Keybindings.md)
 
+## Comparing a file in a previous revision with the working copy
+
+When navigating the commits, select a file, and press 'f' to compare it with the git difftool against the working copy.
+
+Does not work with renamed files though.
+
+```yml
+customCommands:
+  - key: 'f'
+    command: "git difftool {{.SelectedLocalCommit.Sha}} -- {{.SelectedCommitFile.Name}}"
+    context: 'commitFiles'
+    description: 'Compare (difftool) with local copy'
+```
+
 ## Creating a review in [Gerrit](https://gerrit-review.googlesource.com/Documentation/intro-gerrit-walkthrough.html)
 
 ```yml