demos: add blank line at the end

This makes it slightly easier to take a screenshot without getting the
cursor character from the shell input line just below.

demos/demo_git_compat.sh

@@ -14,3 +14,5 @@ run_command "jj diff -r b1"
 
 comment "The repo is backed by the actual Git repo:"
 run_command "git --git-dir=.jj/repo/store/git log --graph --all --decorate --oneline"
+
+blank

demos/demo_juggle_conflicts.sh

@@ -44,3 +44,5 @@ run_command "jj log"
 comment "Again, because the merge commit has the
 changes from all three commits, it has no
 conflict."
+
+blank

demos/demo_operation_log.sh

@@ -50,3 +50,5 @@ run_command "jj op restore $rebase_op"
 comment "We're now back to before the \"other stuff\"
 change existed:"
 run_command "jj log"
+
+blank

demos/demo_resolve_conflict.sh

@@ -38,3 +38,5 @@ run_command "echo \"Hello earth!\" > README"
 
 comment "The status command no longer reports it:"
 run_command "jj status"
+
+blank

demos/demo_working_copy.sh

@@ -46,3 +46,5 @@ run_command "jj describe goodbye -m goodbye"
 
 comment "Inspect the result:"
 run_command "jj log"
+
+blank