Update theme customization

- Move the env.md from /env directory to be displayed in the theming
section
- Update copy to remove references to downstream changes since changes
are made upstream

Signed-off-by: Derick Montague <derick.montague@ibm.com>
Change-Id: I5ed3c62a9534c071b6dbd7f69ed35d457353a628
diff --git a/docs/.vuepress/config.js b/docs/.vuepress/config.js
index 8b7be97..9043606 100644
--- a/docs/.vuepress/config.js
+++ b/docs/.vuepress/config.js
@@ -53,7 +53,7 @@
           ]
           }
         ],
-        "/themes/": ["", "customize"]
+        "/themes/": ["", "customize", "env"]
       },
     },
     configureWebpack: {