Add git clean/smudge commands to README

Author: thejpster

README.md

@@ -284,6 +284,19 @@ Why not design and build your own expansion card? You could try designing:
 
 See [CHANGELOG.md](./CHANGELOG.md) for a list of detailed changes.
 
+## Git Setup
+
+We recommend you have the following Git config set:
+
+```
+$ git config --global filter.kicad_project.clean "sed -E 's/^update=.*$/update=Date/'"
+$ git config --global filter.kicad_project.smudge cat
+$ git config --global filter.kicad_sch.clean "sed -E 's/#(PWR|FLG)[0-9]+/#\1?/'"
+$ git config --global filter.kicad_sch.smudge cat
+```
+
+See https://jnavila.github.io/plotkicadsch/ for details.
+
 ## Licence
 
 This schematic and PCB design is Copyright (c) The Neotron Developers.