avoid leaving the git repository in a detached state

README.md

@@ -62,9 +62,10 @@ révision, il faut effectuer les opérations suivantes:
 git checkout main
 cp make_single_short.pl tmp.pl
 ./make_single_short.pl > expanded_short.tex
-git checkout e92dfdf9
+git checkout e92dfdf9 # choose you own revision identifier here
 ./tmp.pl > old_expanded_short.tex
 latexdiff old_expanded_short.tex expanded_short.tex > pre_diff.tex
 sed -e "/DIF/s/.url//" pre_diff.tex > diff.tex
 pdflatex diff
+git checkout main
 ```