Print the first-time path for a new branch on the work PC

The work-PC instructions began with 'git checkout <branch>', which fails the
first time a branch goes over because it does not exist in that clone yet -
exactly the moment somebody follows them most carefully. Nothing to check out,
and nothing to merge into either.

Now prints both: fetch then checkout -b then push -u the first time, and the
checkout/fetch/merge/push cycle afterwards.

Scope: product

tools/export-github.sh

@@ -274,10 +274,20 @@ fi
 cat <<EOF
 
 On the work PC (in the shopdb-flask-pub clone):
-  git checkout $BRANCH
-  git fetch <path-to>\shopdb-flask-pub-$BRANCH.bundle $BRANCH
-  git merge --ff-only FETCH_HEAD
-  git push origin $BRANCH
+
+  The FIRST time this branch goes over - it does not exist there yet, so
+  there is nothing to check out and nothing to merge into:
+
+    git fetch <path-to>\shopdb-flask-pub-$BRANCH.bundle $BRANCH
+    git checkout -b $BRANCH FETCH_HEAD
+    git push -u origin $BRANCH
+
+  Every time after that:
+
+    git checkout $BRANCH
+    git fetch <path-to>\shopdb-flask-pub-$BRANCH.bundle $BRANCH
+    git merge --ff-only FETCH_HEAD
+    git push origin $BRANCH
 EOF
 
 if [ "$BRANCH" != "main" ]; then