Added docs for using schema in Python client lib (#3511)
Added docs for using schema in Python client lib (#3511)

* Added docs for using schema in Python client lib

* Added info on required fields

merlimat/pulsar,nkurihar/pulsar,massakam/pulsar,nkurihar/pulsar,merlimat/pulsar,nkurihar/pulsar,massakam/pulsar,nkurihar/pulsar,yahoo/pulsar,nkurihar/pulsar,yahoo/pulsar,nkurihar/pulsar,massakam/pulsar,massakam/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,merlimat/pulsar,merlimat/pulsar,yahoo/pulsar,nkurihar/pulsar,merlimat/pulsar,merlimat/pulsar,nkurihar/pulsar,nkurihar/pulsar