Create README (#294)

* Create README

issue #157
Would appreciate review for correct use of language, relevance of links, content, etc.

Signed-off-by: maryaB-osr <[email protected]>

* Changed command/verb usage and included add command tutorial

Signed-off-by: Marya <[email protected]>

Author: maryaB-osr

README.md

@@ -0,0 +1,27 @@
+# ros2cli
+
+This repository contains the source code for ROS 2 command line interface tools included with a standard install of any ROS 2 distro.
+
+## Usage
+
+Run `ros2 --help` to see all available commands.
+
+Run `ros2 <command> --help` for more information on individual command usage.
+
+Run `ros2 <command> <verb> --help` for even more usage information on a specific command's verbs.   
+
+Read [Introspection with command line tools](https://index.ros.org/doc/ros2/Tutorials/Introspection-with-command-line-tools/) on ROS Index for more information and an example.
+
+### Cheat Sheet
+
+This [cheat sheet](https://github.com/artivis/ros2_cheats_sheet/blob/master/cli/cli_cheats_sheet.pdf) provides examples for commands and their verbs (some of which rely on the [ROS 2 demos package](https://github.com/ros2/demos)).
+
+## Add New Verbs
+
+You can use [Python entry points](https://setuptools.readthedocs.io/en/latest/pkg_resources.html#entry-points) to create new commands and verbs for the CLI.
+[Here's an example](https://github.com/ros2/ros2cli/pull/273/files).
+And [here's and example](https://github.com/artivis/ros2hellocli) for how to add a command.
+
+## Background
+
+You can find a [historical discussion](https://discourse.ros.org/t/ros-graph-information-tools-implementation-discussion/674/34) on this subject on Discourse.