sbt: add README (#7294)

plugins/sbt/README.md

+# sbt plugin
+
+This plugin adds completion for the [sbt, the interactive build tool](https://scala-sbt.org/),
+as well as some aliases for common sbt commands.
+
+To use it, add `sbt` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... sbt)
+```
+
+## Aliases
+
+| Alias | Command               | Description                                                  |
+|-------|-----------------------|--------------------------------------------------------------|
+| sbc   | `sbt compile`         | Compiles the main sources                                    |
+| sbcln | `sbt clean`           | Deletes all generated files                                  |
+| sbcc  | `sbt clean compile`   | Deletes generated files, compiles the main sources           |
+| sbco  | `sbt console`         | Starts Scala with the compiled sources and all dependencies  |
+| sbcq  | `sbt console-quick`   | Starts Scala with all dependencies                           |
+| sbcp  | `sbt console-project` | Starts Scala with sbt and the build definitions              |
+| sbd   | `sbt doc`             | Generates API documentation for Scala source files           |
+| sbdc  | `sbt dist:clean`      | Deletes the distribution packages                            |
+| sbdi  | `sbt dist`            | Creates the distribution packages                            |
+| sbgi  | `sbt gen-idea`        | Create Idea project files                                    |
+| sbp   | `sbt publish`         | Publishes artifacts to the repository                        |
+| sbpl  | `sbt publish-local`   | Publishes artifacts to the local Ivy repository              |
+| sbr   | `sbt run`             | Runs the main class for the project                          |
+| sbrm  | `sbt run-main`        | Runs the specified main class for the project                |
+| sbu   | `sbt update`          | Resolves and retrieves external dependencies                 |
+| sbx   | `sbt test`            | Compiles and runs all tests                                  |
+| sba   | `sbt assembly`        | Create a fat JAR with all dependencies                       |