Create README.md

API Reference:
- Autocomplete: /autocomplete?start=<<PREFIX>>
-- Multiple words should be separated by + e.g. 'short+bones'

- Retrieve HPO: /hpo?id=<<HPO ID>> (e.g., HP:0009381)
- Retrieve MeSH: /mesh?id=<<MESH ID>> (e.g., D012779)
- Retrieve Pub: /pmid?id=<<PUBMED ID>> (e.g., 12921311)
- Search: /search?hpo=<<HPO ID, HPO ID, ...>> & mesh=<<MESH ID, MESH ID, ...>>