This commit improves the meta descriptions for several pages by making them dynamic and object-specific.
- The default meta description in `app/views/layouts/_head.html.haml` has been updated to include a mention of open data.
- The `show.html.haml` views for crops, seeds, plantings, harvests, and members now have a `content_for :meta_description` block. This block uses the object's description or bio if available, and falls back to a generated string if not.
