Update documentation for generating SSL for Apple's new extendedKeyUsage

[chench00]

Describe the Bug

Steps To Reproduce

1. Follow install instructions for Bitwarden Linux
2. Generate SSL certificate without domain
3. Import certificate into iOS device and instal
4. Try and log in to the Bitwarden app and it doesn't work

Expected Result

Login successfully

Actual Result

The certificate for this server is invalid.

Screenshots or Videos

Environment

• Device: iPhone XS MAX
• Operating system: iOS 13
• Build Version (go to "Settings" → "About" in the app): Can't see as I can't login
• Is this a Beta release? N

Additional Context

I am following the instructions here for trying and update my certificate with the new extendedKeyUsage flag requirement but nothing here mentions how to achieve it.

If someone could provide instructions for achieving this would be greatly appreciated.

[vvolkgang]

Issue migrated to bitwarden/mobile#1028