Fix typo in README.md

[elvis-sik]

Description

Fix minor typo: accesible should be accessible.

Affected Dependencies

Not relevant.

How has this been tested?

• Googled to check proper spelling :)

Checklist

• [X] I have followed the Contribution Guidelines and Code of Conduct
• [X] I have commented my code following the OpenMined Styleguide
• [ ] I have labeled this PR with the relevant Type labels
• [X] My changes are covered by tests