Fixed "SecureUser" references in documentation

[elithrar]

I've fixed a couple of inconsistencies between the documentation in the README and the implementation of SecureUser.

Previously: the docs referred to SecureUserFunc, which does not exist. I've changed the docs to properly use SecureUser in the example when passing additional user details.

I've also updated the Google example to include the additional user details as a second route under /private/user and corrected a discrepancy between the Google example docs and the actual flag expected in the example (now properly refers to access_key).

The examples run and work as expected. I've attempted to copy the existing approach/templates where possible to maintain a consistent style.