Main should be a place for libraries, not sources

The main should contain files that can be used as library, not as sources. They can also contain the sources in forms of `less`, `sass`, or even `d.ts` files, so that the consuming party can choose based on filetype what to use and include in the project. Arguably even `.min.js` can also be added as it's the 'definitive' version of a 'compiled' library.

See also twbs/bootstrap compliance to the spec issues: twbs/bootstrap#16663

README.md

@@ -47,7 +47,7 @@ The package's semantic version number.
 *Recommended*  
 Type: `String` or `Array` of `String`
 
-The entry-point files necessary to use your package. Only one file per filetype.
+The entry-point files necessary to use your package. Only one file per filetype. The files that are offered should be representing your package as library. This means that the files can be used without compiling for use by the consuming party.
 
 Entry-point files have module exports and may use module imports. While Bower does not directly use `main` files, they are listed with the commands `bower list --json` and `bower list --paths`, so they can be used by build tools.
 
@@ -81,6 +81,10 @@ Let's say your package looks like this:
 "main": [
   "js/motion.js",
   "sass/motion.scss",
+  "img/motion.png",
+  "fonts/icons.woff",
+  "fonts/icons.woff2",
+  "dist/movement.css"
 ]
 ```