📝(doc) update docs to install published packages + contributing guide

Updated various parts of existing documentations to make a clean path
to learn how to install the library. I let the most complicated part in
the tokens's README.md file, which is referenced from the Storybook.

packages/react/.storybook/preview.js

@@ -11,6 +11,7 @@ export const parameters = {
   options: {
     storySort: (a, b) => {
       const roots = ['Getting Started', 'Components'];
+      const gettingStartedOrder = ['Installation', 'Colors', 'Spacings', 'Typography'];
 
       const aParts = a.title.split('/');
       const bParts = b.title.split('/');
@@ -18,6 +19,9 @@ export const parameters = {
         return roots.indexOf(aParts[0]) - roots.indexOf(bParts[0]);
       }
       if (aParts[1] !== bParts[1]) {
+        if (aParts[0] === 'Getting Started') {
+          return gettingStartedOrder.indexOf(aParts[1]) - gettingStartedOrder.indexOf(bParts[1]);
+        }
         return aParts[1].localeCompare(bParts[1]);
       }
       return 0;