taste.md: list other sites in bulleted list
taste.md: mention Code Codex site
taste.md: fix html title

Should have been done in 1e8c2775ea4227f3e3062d122f07b27d02066fab.
learn/index.md: mention Code Codex site

Should have been done in be5cf1a7abfd3c1dc9b39d5324b2d0d52be40c58.