docs: add sdm readme

Include original rationale for the SDM (Software-defined mining) crate.

libs/sdm/README.md

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+### The problem
+
+We have a dispersed integration between the backend and frontend: a set of methods that called independently to control
+images and containers. The state of running containers managed partially by both parts that makes debugging too
+difficult.
+
+Also we use multiple instances to interact with docker: `Workspaces`, `DockerWrapper`, an `AppState` with a `Docker`
+instance inside the wrapper, and global standalone `Docker` instance.
+
+There is no a single part responsible for managing containers. For example, we have to monitor docker's events to
+subscribe for a GRPC stream from a wallet container that makes UI's code confusing and tricky for debugging.
+
+### The solution
+
+We need a single self-sufficient crate to manage a set of images and containers to maintain a node of the Tari Network.
+
+That crate could provide a universal abstraction for controlling a deployment of Tari products (Base Node, Mining Node,
+Wallet). The unified approach gives serious benefits:
+
+- Easy unit tests coverage
+- Compatibility with different systems (not only Docker, but also Kubernetes)
+- Support connections to remote clusters
+- CLI Launchpad (for testing purposes)
+- Single synchronized state of containers
+- One channel with events (not necessary to track connections for launched containers manually)
+- Can be used for Web UI as well
+- Can be a part of SaaS infrastructure (in case if we will decide to offer nodes as a service)
+
+#### Implementation
+
+The library can be implemented as a crate that has a method to get a stream of events and a method to send events.
+
+The crate could work as a library and as a binary CLI tool.
+
+#### Tauri Platform integration
+
+For using the crate with the `tauri` platform we could add a method to subscribe to that stream of events that will be
+forwarder to `tauri` events bus. Control events could be sent using a method call.