update column extension function names and desc in readme

[fatemetardasti96]

Proposed changes

Update README with the correct function names. Related to the issue #238

Types of changes

What types of changes does your code introduce to quinn?
Put an x in the boxes that apply

• Bugfix (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 not work as expected)
• Documentation Update (if none of the other choices apply)

[SemyonSinchenko]

LGTM. Thanks for the contribution, @fatemetardasti96 !