Improve error message and docs for the SOAR certifi issue

I'd noted this issue in setup friction: https://github.com/google/mcp-security/issues/123

but I've had 2 new reports on it in as many days, so I think it needs higher priority.

We note the problem and solution in: https://google.github.io/mcp-security/usage_guide.html#mcp-server-configuration-reference

Additionally, for the secops-soar MCP server, you will need use the CA list bundled with the certifi package. This can be done via the following command. Change the Python minor version to match whatever version you are currently running. (ex. Python\ 3.11): /Applications/Python\ 3.12/Install\ Certificates.command

We should:

1. Include that in the readme.
2. Catch the error and print something more meaningful.

The message printed now is:

Failed to fetch valid scopes from SOAR, please make sure you have configured the right SOAR credentials.

We can trap that and verify the certifi issue and then print a much more meaningful message.

I'm marking this as good-first-issue but a pull request MUST include evidence before/after showing that the new error messages is working.