add README

Signed-off-by: Johnson Shi <Johnson.Shi@microsoft.com>

README.md

@@ -0,0 +1,32 @@
+# ORAS Tools
+
+Helper tools for [ORAS](https://oras.land).
+
+## Quick Start
+
+### Install
+
+To install, run the following commands.
+
+```bash
+curl -LO https://github.com/johnsonshi/oras-tools/releases/download/v0.0.1/oras-tools
+chmod +x oras-tools
+sudo mv oras-tools /usr/local/bin
+```
+
+## Commands
+
+### Delete
+
+Delete [ORAS artifacts](https://oras.land/#how-oras-works) from a registry.
+
+To delete an ORAS artifact (referenced by its hash `$digest`) in `$registry_url` and `$repository_name`:
+
+```bash
+./bin/oras-tools delete \
+  --username "$registry_username" \
+  --password "$registry_password" \
+  --registry "$registry_url" \
+  --repository "$repository_name" \
+  --digest "$digest"
+```