Add npm-naming documentation

docs/npm-naming.md

@@ -0,0 +1,67 @@
+# npm-naming
+
+(This rule is specific to DefinitelyTyped.)
+
+Checks that the name of the type package matches a source package on npm.
+
+---
+
+**Bad**:
+
+```ts
+// Type definitions for browser-only-package 1.2
+```
+
+* If the package is really browser-only, you have mark it with "non-npm package"
+* If the package actually has a matching npm package, you must use that name.
+
+**Good**:
+
+```ts
+// Type definitions for non-npm package browser-only-package 1.2
+```
+
+---
+
+**Bad**:
+
+```ts
+// Type definitions for some-package 101.1
+```
+
+* The version number in the header must actually exist on npm for the source package.
+
+**Good**:
+
+```ts
+// Type definitions for some-package 10.1
+```
+
+---
+
+**Bad**:
+
+`foo/index.d.ts`:
+
+```ts
+declare function f(): void;
+export default f;
+```
+
+`foo/index.js`:
+
+```js
+module.exports = function () {
+};
+```
+
+* A commonjs module.exports assignment is not really an export default, and the d.ts should use the `export =` syntax.
+
+**Good**:
+
+`foo/index.d.ts`:
+
+```ts
+function f(): void;
+export = f;
+```