Update Readme.md with password expiration workaround

[piranout]

The Readme mentions that:

If you are using a username and password and you change your password, you cannot update your password (clicking Configure for the server doesn't work again). You have to remove all projects and add the server again.

Users can avoid this. Simply use a Jenkins-issued API Token instead of your password.

1. Log into Jenkins
2. Click your username (in the upper right corner)
3. Click Configure (in the left navbar)
4. Click Show API Token
5. Use this token in place of your password when setting up the Jenkins Transport settings

[csnate]

What version of Jenkins are you using?

[piranout]

Works in 2.18 and 2.20, at least.

[csnate]

Cool! Readme updated.