Updated serve help, refs #1028

docs/datasette-serve-help.txt

@@ -18,7 +18,7 @@ Options:
                             useful for development
 
   --cors                    Enable CORS by serving Access-Control-Allow-Origin: *
-  --load-extension PATH     Path to a SQLite extension to load
+  --load-extension TEXT     Path to a SQLite extension to load
   --inspect-file TEXT       Path to JSON file created using "datasette inspect"
   -m, --metadata FILENAME   Path to JSON/YAML file containing license/source metadata
   --template-dir DIRECTORY  Path to directory containing custom templates