Fix typos in DDP tutorial

[tholop]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Docs change / refactoring / dependency upgrade

Motivation and Context / Related issue

I was reading the DDP tutorial and spotted a few typos. Great write-up by the way!

Checklist

• The documentation is up-to-date with the changes I made.
• I have read the CONTRIBUTING document and completed the CLA (see CONTRIBUTING).
• All tests passed, and additional code has been covered with new tests.

[facebook-github-bot]

@romovpa has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.