Update examples for metadata fetch and search APIs

Both the examples at the moment don't give any results which can be confusing for anyone:

• https://archive.softwareheritage.org/api/1/origin/metadata-search/?limit=2&fulltext=Jane%20Doe
• https://archive.softwareheritage.org/api/1/origin/https://github.com/python/cpython/intrinsic-metadata/

However, the new ones will have some data:

• https://archive.softwareheritage.org/api/1/origin/metadata-search/?limit=2&fulltext=node-red-nodegen
• https://archive.softwareheritage.org/api/1/origin/https://github.com/node-red/node-red-nodegen/intrinsic-metadata