updated language for import/ignore setting (ref #103)

README.md

@@ -341,18 +341,24 @@ You may set the following settings in your `.eslintrc`:
 #### `import/ignore`
 
 A list of regex strings that, if matched by a path, will
-not parse the matching module. In practice, this means rules other than
-`no-unresolved` will not report on the `import` in question.
+not report the matching module if no `export`s are found.
+In practice, this means rules other than `no-unresolved` will not report on any
+`import`s with (absolute) paths matching this pattern, _unless_ `export`s were
+found when parsing. This allows you to ignore `node_modules` but still properly
+lint packages that define a [`jsnext:main`] in `package.json` (Redux, D3's v4 packages, etc.).
 
-This will replace the default of `node_modules`, so you may need to include it in your own list. Example:
+**Note**: setting this explicitly will replace the default of `node_modules`, so you
+may need to include it in your own list if you still want to ignore it. Example:
 
 ```yaml
 settings:
   import/ignore:
-    - node_modules
-    - coffee$
+    - node_modules  # mostly CommonJS (ignored by default)
+    - \.coffee$     # fraught with parse errors
 ```
 
+[`jsnext:main`]: https://github.com/rollup/rollup/wiki/jsnext:main
+
 #### `import/resolver`
 
 See [resolver plugins](#resolver-plugins).