Add 'custom' key for DB .source property to make origin or MIME type …

…more explicit.

README.md

@@ -49,10 +49,10 @@ The JSON file is a map lookup for lowercased mime types.
 Each mime type has the following properties:
 
 - `.source` - where the mime type is defined.
-    If not set, it's probably a custom media type.
     - `apache` - [Apache common media types](http://svn.apache.org/repos/asf/httpd/httpd/trunk/docs/conf/mime.types)
     - `iana` - [IANA-defined media types](http://www.iana.org/assignments/media-types/media-types.xhtml)
     - `nginx` - [nginx media types](http://hg.nginx.org/nginx/raw-file/default/conf/mime.types)
+    - `custom` - Loaded from custom set of types maintained in this repository.
 - `.extensions[]` - known extensions associated with this mime type.
 - `.compressible` - whether a file of this type can be gzipped.
 - `.charset` - the default charset associated with this type, if any.

scripts/build.js

@@ -11,7 +11,7 @@ addData(db, require('../src/apache-types.json'), 'apache')
 addData(db, require('../src/nginx-types.json'), 'nginx')
 
 // now add all our custom data
-addData(db, require('../src/custom-types.json'))
+addData(db, require('../src/custom-types.json'), 'custom')
 
 // finally, all custom suffix defaults
 var mime = require('../src/custom-suffix.json')