text: Title: Docs - porting from flask-jwt
  Body: Thanks for the hard work.
  
  Looking though the docs it appears this extension is similar to flask-jwt but not identical.  Would be nice to have a section in the docs on how to port to the newer library and any associated concerns there might be.  So far I've noticed:
  
  - JWT --> JWTManager(app)
  - Need to create an auth view method 
  - Config: 
  
    - JWT_AUTH_HEADER_PREFIX  --> JWT_HEADER_TYPE
    - JWT_EXPIRATION_DELTA -->  JWT_ACCESS_TOKEN_EXPIRES
  
  - No leeway
  
  Is that a good start?