Port CLI readme (#1031)

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tools/cli/README.md

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+# Foundry CLIs
+
+An artifact containing basic CLI utilities for Kotlin.
+
+## Installation
+
+[![Maven Central](https://img.shields.io/maven-central/v/com.slack.foundry/cli.svg)](https://mvnrepository.com/artifact/com.slack.foundry/cli)
+```kotlin
+// In Gradle
+dependencies {
+  implementation("com.slack.foundry:cli:<version>")
+}
+
+// In kotlin script
+@file:DependsOn("com.slack.foundry:cli:{version}")
+```
+
+## Local testing
+
+If consuming these utilities from a kotlin script file, you can test changes like so:
+
+1. Set the version in `gradle.properties`, such as `2.5.0-LOCAL1`.
+2. Run `./gradlew publishToMavenLocal` to publish the current version to your local maven repository.
+3. In your script file, add the local repository and update the version:
+    ```kotlin
+    @file:Repository("file:///Users/{username}/.m2/repository")
+    @file:DependsOn("com.slack.foundry:cli:{version you set in gradle.properties}")
+    ```
+4. Repeat as needed while testing, incrementing the version number each time to avoid caching issues.