Reword kernel.event_listener description

[wouterj]

In the DIC tags reference, we should reword the description of the kernel.event_listener tag. Currently, it can be understood wrongly as something that's only meant for core things.

Thanks to our IRC friends for reporting this issue!

ChairmanOfBoard: What I stumped at, was that it seemed like kernel.event_listener was just for core events, and that somehow I felt maybe one should create their own event dispatcher outside the main one
Lumbendil: no
Lumbendil: what made you think such a thing? :)
ChairmanOfBoard: This doc
ChairmanOfBoard: http://symfony.com/doc/current/reference/dic_tags.html
ChairmanOfBoard: For example, if you have a service that you would like to register as a listener to one of Symfony's core events, you can flag it with the kernel.event_listener tag.
ChairmanOfBoard: I don't think I thought enough about that line, and took it the wrong way
ChairmanOfBoard: Also the name "kernel.event_listener" makes it sound like its just for kernel events

[bicpi]

@wouterj I don't quite get what is confusing here. Is it the description in the overview table at the beginning or the detailed description?

[wouterj]

It's not the documentation that is confusing, it's the name of the tag. As we can't rename the tag simply, we should make it clear to explicitely tell them that this tag is for your own listeners/subscribers.

[javiereguiluz]

I'm trying to reword this content in #5445 but I don't know if the new explanation is better than the existing one.