doc: adding first readme documentation steps

Author: simschla

README.md

@@ -3,6 +3,7 @@
 [![Gradle Plugin](https://img.shields.io/gradle-plugin-portal/v/com.diffplug.spotless?color=blue&label=gradle%20plugin)](plugin-gradle)
 [![Maven Plugin](https://img.shields.io/maven-central/v/com.diffplug.spotless/spotless-maven-plugin?color=blue&label=maven%20plugin)](plugin-maven)
 [![SBT Plugin](https://img.shields.io/badge/sbt%20plugin-0.1.3-blue)](https://github.com/moznion/sbt-spotless)
+[![CLI](https://img.shields.io/badge/cli-0.0.1-blue)](cli)
 
 Spotless can format <antlr | c | c# | c++ | css | flow | graphql | groovy | html | java | javascript | json | jsx | kotlin | less | license headers | markdown | objective-c | protobuf | python | scala | scss | shell | sql | typeScript | vue | yaml | anything> using <gradle | maven | sbt | anything>.
 
@@ -41,6 +42,13 @@ user@machine repo % mvn spotless:check
 ```
 
 ## [❇️ Spotless for SBT (external for now)](https://github.com/moznion/sbt-spotless)
+
+## [❇️ Spotless Command Line Interface (CLI)](cli)
+
+```console
+user@machine repo % spotless --target '**/src/**/*.java' license-header --header='/* Myself $YEAR */' google-java-format
+```
+
 ## [Other build systems](CONTRIBUTING.md#how-to-add-a-new-plugin-for-a-build-system)
 
 ## How it works (for potential contributors)

cli/README.md

@@ -0,0 +1,25 @@
+# <img align="left" src="../_images/spotless_logo.png"> Spotless Command Line Interface CLI
+*Keep your code Spotless with Gradle*
+
+<!---freshmark shields
+output = [
+  link(shield('Changelog', 'changelog', '{{versionLast}}', 'blue'), 'CHANGES.md'),
+  '',
+  link(shield('OS Win', 'OS', 'Windows', 'blueviolet'), 'README.md'),
+  link(shield('OS Linux', 'OS', 'Linux', 'blueviolet'), 'README.md'),
+  link(shield('OS macOS', 'OS', 'macOS', 'blueviolet'), 'README.md'),
+  ].join('\n');
+-->
+[![Changelog](https://img.shields.io/badge/changelog-0.0.1-blue.svg)](CHANGES.md)
+
+[![OS Win](https://img.shields.io/badge/OS-Windows-blueviolet.svg)](README.md)
+[![OS Linux](https://img.shields.io/badge/OS-Linux-blueviolet.svg)](README.md)
+[![OS macOS](https://img.shields.io/badge/OS-macOS-blueviolet.svg)](README.md)
+<!---freshmark /shields -->
+
+`spotless` is a command line interface (CLI) for the [spotless code formatter](../README.md).
+It intends to be a simple alternative to its siblings: the plugins for [gradle](../plugin-gradle/README.md), [maven](../plugin-maven/README.md)
+and others. 
+
+- TODO: add usage and examples
+- TBD: can usage be generated automatically e.g. via freshmark?