export-chrome-bookmarks.sh: added usage info

export-chrome-bookmarks.sh

@@ -1,10 +1,20 @@
 #!/usr/bin/env nix-shell
-#!nix-shell --pure -i bash -p dejsonlz4 jq bash -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/fea633695211167753ee732c9087808d0c57461c.tar.gz
-
-# Usage: ./export-firefox-bookmarks.sh [path/to/.mozilla/firefox/XXXXXXXX.profile]
+#!nix-shell --pure -i bash -p jq bash -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/fea633695211167753ee732c9087808d0c57461c.tar.gz
 
 set -euET -o pipefail
 
+usage() {
+  printf "Usage: %q [path/to/.config/chromium/Default/]"\\n "$0"
+}
+
+if test $# -ne 1; then
+  usage
+  exit 1
+elif test $# -eq 1 && (test "x$1" = "x-h" || test "x$1" = "x--help"); then
+  usage
+  exit 0
+fi
+
 if test $# -ge 1; then
   profile="$1"
 else