[README] Rename "context" to "system architecture"

[Zelig880]

When reading the readme, the context section does not actually look like a context, but it explain the architecture of the system

AC:

• Create a new Document called "system-architecture" in the "document" folder and move all the "context" content into it
• Rename "context" to "system architecture"
• In the current list of context (that is now moved in the other file), change the point 4 to actually inform that the user is notified when they log in. The way it is written now, it seems like the notification happen offline.
• On the point 5, not sure if you want to say that the user has to manually withdraw their win because we are not using an escrow account based architecture and probably provide an external link for it.
• Add a paragraph within the main readme under the "system architecture" that includes:
  • The "Build With" section
  • A paragraph that informs that the project was structured to be easy to follow and read.
  • Another paragraph to say that if they want to have more information about the technicalities, the system diagram and file structure, they can go to the system architecture document and link the new document created above