README grammar/clarity fixes

[omccully]

What this PR does / why we need it:

I was reading the README and I came across a section that seemed like it was written by a non-native English speaker (lines 445-446), so I started fixing that. Then I proof-read the rest of the readme file to see what else there was.

Which issue(s) this PR fixes:

No issue created.

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Readme only.

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• [x] Code compiles correctly
• [x] Created/updated tests
• [x] Unit tests passing
• [x] End-to-end tests passing
• [x] Extended the documentation
• [x] Provided sample for the feature