docs(readme): make node 12 requiremen explicit

add warning about projects-storage.eclipse.org connection

README.md

@@ -37,6 +37,11 @@ Eclipse Theia Blueprint is ***not*** **a production-ready product**. Therefore,
 
 ## Development
 
+### Requirements
+- node 12 
+- python 3
+- yarn
+
 ### Documentation
 
 Documentation on how to package Theia as a Desktop Product may be found [here](https://theia-ide.org/docs/blueprint_documentation/)
@@ -66,6 +71,10 @@ The packaged application is located in `applications/electron/dist`.
 
 ### Create a preview application (without packaging it)
 
+**Known Issue** 
+It is possible that during the `package:preview` step users encounter an error, see [#132](https://github.com/eclipse-theia/theia-blueprint/issues/132). 
+This error should not impede the bundling native to your OS, which can be used to testing etc.        
+
 ```sh
 yarn electron package:preview
 ```