improve readme by adding contact email for security issues

[sredxny]

Description

In the readme add the contact email for those cases where a security is discovered by one of the contributors/users

Related Issue

Motivation and Context

How This Has Been Tested

Screenshots (if appropriate)

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)

Checklist

• Make sure you are requesting to pull a topic/feature/bugfix branch (right side). If pulling from your own
  fork, don't request your master!
• Make sure you are making a pull request against the master branch (left side). Also, you should start
  your branch off our latest master.
• My change requires a change to the documentation.
  • If you've changed APIs, describe what needs to be updated in the documentation.
• I have updated the documentation accordingly.
• Modules and vendor dependencies have been updated; run go mod tidy && go mod vendor
• I have added tests to cover my changes.
• All new and existing tests passed.
• Check your code additions will not fail linting checks:
  • go fmt -s
  • go vet

[padiazg]

Addition looks good to me, but seems like there's a previous issue in the doc