Document _mq.scss mixins for css based layout breakpoints

[epelc]

Proposal

What is the summary of the proposal?

Right now you have to search the source or npm installed files to find out that there are sass mixins for the builtin layout breakpoints which you can use in scss/sass for your own styles. These are very convenient especially if you come from the old angularJS material project which included something similar as variables.

What is the proposal?

Document existance of _mq.scss file and that it's generated from src/lib/core/sass/_layout-bp.scss.

ie add it to the wiki with the example from comments

You can import in a project via

@import '@angular/flex-layout/_mq';

@include layout-bp(sm) {
    color: red;
}

Is there anything else we should know?

Perhaps this issue will be enough documentation/pointing it out for others.