update readme

Author: Porges

README.md

@@ -1,2 +1,15 @@
 # html2rdf
-A Rust library for reading RDFa data from HTML.
+
+A Rust library & CLI for reading RDFa data from HTML.
+
+## Installation
+
+```console
+$ cargo install html2rdf-cli
+```
+
+## CLI usage
+
+```console
+$ html2rdf http://games.porg.es/games/tic-tac-toe
+```