demos: set title when creating recording

According to asciinema.org, it should be possible to change the title
after uploading, but I couldn't figure out how to do that. Let's set
it when creating the recording. That also means it's one less step to
perform when re-running scripts.

demos/demo_git_compat.sh

@@ -5,7 +5,7 @@ parse_args "$@"
 
 new_tmp_dir
 
-run_demo '
+run_demo 'Clone a Git repo' '
 run_command "# Clone a Git repo:"
 run_command "jj git clone https://github.com/octocat/Hello-World"
 run_command "cd Hello-World"

demos/demo_helpers.sh

@@ -44,9 +44,10 @@ new_tmp_dir() {
 }
 
 run_demo() {
-    local expect_script="$1"
+    local title="$1"
+    local expect_script="$2"
     expect_script=$(printf "source $BASE_DIR/demo_helpers.tcl
-spawn asciinema rec -c \"PS1='$ ' bash --norc\"
+spawn asciinema rec -c \"PS1='$ ' bash --norc\" --title \"$title\"
 expect_prompt
 %s
 quit_and_dump_asciicast_path