Clarification of the neccessary autoloading of plugins...

...in the error message

Added links to the relevant documentation
I intended to keep the style of the error messages as they are.
I could not find the use of an element in an error message altogether - excluding the stack trace at the bottom.
The original content was duplicated already!

This proposed change would hit many other error messages and has nothing to do with this current issue. Nether the less I am not sure if it is good to do so anyway, as it might complicate following the origin of the message.