Add link to & from Juno from main site jsoftware.com

[sohang3112]

• Main jsoftware docs (https://www.jsoftware.com/#/README) don't mention / link to this Juno IDE anywhere. It should mention Juno IDE site (https://jsoftware.github.io/juno/app/) as online alternative to downloading J.
• Juno IDE site should also link to JSoftware main docs site.