[docs] add mvp scope outline, flow diagram

docs/mvp

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+scope for mvp
+
+features
+- turn daemon on and off in headerbar
+- click "send file" and select file in file chooser to send file
+- notification on receiver side to confirm
+- notification on receiver side when transfer is complete
+
+- avahi service publishing and discovery
+- open and close http server
+- download from url
+
+
+not in scope
+- popovers for settings and name
+- displaying files in ui
+- drag and drop to send