Update README.md

[yashmeet29]

Describe your changes

This PR updates ReadMe for custom properties support in plugin

Type of change

Please delete options that are not relevant.

• 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 not work as expected)
• This change requires a documentation update
• ReadMe update

Checklist before requesting a review

• [N/A] I have tested the functionality on my cloud environment.
• [N/A] I have provided sufficient automated/ unit tests for the code.
• [N/A] I have increased or maintained the test coverage.
• [N/A] I have ran integration tests on my cloud environment.
• [N/A] I have validated blackduck portal for any vulnerability after my commit.

Upload Screenshots/lists of the scenarios tested

• [N/A] I have Uploaded Screenshots or added lists of the scenarios tested in description

[ashishjain14]

LGTM