docs: Fix a few typos

[timgates42]

There are small typos in:

• docs/conf.py
• docs/readme.rst
• stream_framework/tests/storage/base.py

Fixes:

• Should read that rather than shat.
• Should read pollution rather than polution.
• Should read immediately rather than immediatly.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md