docs: Added tutorials

README.md

@@ -20,8 +20,8 @@ Additionally some npm packages are required, run `npm i` to install them
 
 ## Other Requirements
 
- - Ubuntu One account
- - Snapcraft signing key
+ - Ubuntu One account (create at https://login.ubuntu.com/+login)
+ - Snapcraft signing key (tutorial https://tutorials.ubuntu.com/tutorial/create-your-own-core-image#3)
  - Any of the supported boards or at least 4GB RAM free for virtualization
 
 ## Creating the image