Add installation step on readme

Author: seratch

README.md

@@ -6,6 +6,12 @@ Most users can simply follow the guided configuration and installation instructi
 
 ## Installation
 
+You can download [openai-guardrails package](https://pypi.org/project/openai-guardrails/) this way:
+
+```bash
+pip install openai-guardrails
+```
+
 ### Usage
 
 Follow the configuration and installation instructions at [guardrails.openai.com](https://guardrails.openai.com/).