Update README.md

[gilllo]

update bug bounty details in README

Description

Motivation and Context

Does this change the ABI/API?

• This changes the ABI/API

What tests did you add/modify to account for these changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New module / feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I added a changeset to account for this change

Reviewer Checklist:

• My review includes a symposis of the changes and potential issues
• The code style is enforced
• There are no risky / concerning changes / additions to the PR

[iainnash]

Looks good!