clean up readme

[nan-wang]

• [x] crafters
• [x] rankers
• [x] segmenters
• [x] encoders
• [ ] indexers (will fix in another PR)

[tadejsv]

Why are we deleting usage examples?

[nan-wang]

Why are we deleting usage examples?

I remove those that provides no extra information beyond the uses section at hub.jina.ai