chore: update code blocks in readme

[afuetterer]

I updated the code blocks in the readme.

• added "```python" where it was missing
• removed unnecessary "#!/usr/bin/env python" shebangs
• removed "import tika" where not needed, e.g. import tika, from tika import parser
• use tika.tika, where required, e.g. "import tika from tika" is not valid python
• fixed indentation
• reordered imports

What do you think?

[chrismattmann]

LGTM!