Check for common problems when adding the "E-easy"/"E-less easy" labels

[jdm]

The first time the label is added, we should check for the presence of common issues. I need to think about what this involves, but off the top of my head:

• lack of filenames (a/b.rs), types/modules (a::b)
• lack of instructions involving mach (ie. ./mach test-wpt, ./mach build-cef, ./mach test-tidy)

We could leave a comment highlighting the missing pieces and linking to a document with best practices for filing issues intended for non-core contributors.