extra detail about no-duplicates. closes #242

docs/rules/no-duplicates.md

@@ -2,11 +2,19 @@
 
 Reports if a resolved path is imported more than once.
 
+ESLint core has a similar rule ([`no-duplicate-imports`](http://eslint.org/docs/rules/no-duplicate-imports)), but this version
+is different in two key ways:
+
+1. the paths in the source code don't have to exactly match, they just have to point to the same module on the filesystem. (i.e. `./foo` and `./foo.js`)
+2. this version distinguishes Flow `type` imports from standard imports. ([#334](https://github.com/benmosher/eslint-plugin-import/pull/334))
+
 ## Rule Details
 
 Valid:
 ```js
 import SomeDefaultClass, * as names from './mod'
+// Flow `type` import from same module is fine
+import type SomeType from './mod'
 ```
 
 ...whereas here, both `./mod` imports will be reported:
@@ -18,6 +26,9 @@ import SomeDefaultClass from './mod'
 import foo from './some-other-mod'
 
 import * as names from './mod'
+
+// will catch this too, assuming it is the same target module
+import { something } from './mod.js'
 ```
 
 The motivation is that this is likely a result of two developers importing different
@@ -26,5 +37,7 @@ locations in the file.) This rule brings both (or n-many) to attention.
 
 ## When Not To Use It
 
+If the core ESLint version is good enough (i.e. you're _not_ using Flow and you _are_ using [`import/extensions`](./extensions.md)), keep it and don't use this.
+
 If you like to split up imports across lines or may need to import a default and a namespace,
-you may want to disable this rule.
+you may not want to enable this rule.