Update README.md to include the list and rm commands

Author: extremq

README.md

@@ -70,6 +70,19 @@ EOF
 cargo add --registry my-registry some-crate
 ```
 
+### List the crates in the registry
+
+```bash
+# You can also omit --registry by running the command in the registry directory directly
+margo list --registry my-registry-directory
+```
+
+### Remove a crate
+
+```bash
+margo rm --registry my-registry-directory some-crate --version x.y.z
+```
+
 ## Key differences from Crates.io
 
 - 💅 Does not impose file size limits