Update README.md (#25)

README.md

@@ -15,6 +15,9 @@ If you are the one making the modifications, two solutions :
   - either you do it online : you create a branch, modify the files in it
   - either you do it locally (for bigger modifications or reorganization) :
      -  clone the repo locally ```[email protected]:ige-calcul/public-docs.git```
+     -  make sure you create your branch from the latest main branch: \
+       `git checkout main` \
+       `git pull`
      -  create a new branch from main : ```git checkout -b issue_test main```
      -  do your modifications
      -  push your modifications online : ```git push --set-upstream origin issue_test```