If you get a message when trying to add the Read&Write for Google Chrome extension that shows that it is blocked by administrator there are likely restrictions on adding Chrome extensions on the domain your account is setup with.
Chrome administrators would need to refer to following the instructions in this Chrome for enterprise Help article Manage Chrome apps by organizational unit for allowing the extension.
Read&Write for Google Chrome can be allowed by the extension ID and URL:
ID: inoeonmfapjbbkmdafoankkfajkcphgd
URL: https://chrome.google.com/webstore/detail/readwrite-for-google-chro/inoeonmfapjbbkmdafoankkfajkcphgd