add Stem Disintermedia logo (graphql#187)

* add Stem Disintermedia logo

* crop image and remove white background

* crop it a little more

Author: Andy

site/users/index.html.js

@@ -296,6 +296,11 @@ var logos = [
     img: 'artsy.png',
     link: 'https://artsy.github.io/series/react-native-at-artsy/'
   },
+  {
+    name: 'Stem Disintermedia',
+    img: 'stem.png',
+    link: 'https://stem.is'
+  },
   // Adding your logo?
   // Add it to the /users/logos/ directory and then append an entry above this comment.
   //