Add instructions on how to update the certificate file locally

[mfhepp]

Sometimes, the certificate file from Mozilla is more current that the releases of this module.

In order to update the *.pem file locally, I wrote a short script that basically downloads the file from Mozilla and replaces the 'cacert.pem' file by that.

You can find the script here:

https://github.com/mfhepp/update_certifi_certificates

Alternatively, it would be good to include short instructions on how to update the file locally directly with the module.

[sigmavirus24]

No. See #72 (comment)