Add more detail to the README (#253)

Add a quick start section showing how to install and an example section
showing an example running precli against one of the test samples.

---------

Signed-off-by: Eric Brown <ericwb@users.noreply.github.com>

README.md

@@ -1,5 +1,36 @@
-# precli
+# Precli - precaution command line interface
 
 [![Build and Test](https://github.com/securesauce/precli/actions/workflows/unit-test.yml/badge.svg?branch=main)](https://github.com/securesauce/precli/actions/workflows/unit-test.yml)
 
-Precaution command line interface
+Precli is the core of the GitHub App [Precaution](https://github.com/marketplace/precaution) and also a command line interface to demonstate its functionality.
+
+**Quick Start**
+```bash
+pip install precli
+```
+
+**Example**
+
+```
+$ precli tests/unit/rules/python/stdlib/examples/hmac_timing_attack.py
+⛔️ Error on line 18 in tests/unit/rules/python/stdlib/examples/hmac_timing_attack.py
+PY005: Observable Timing Discrepancy
+Comparing digests with the '==' operator is vulnerable to timing attacks.
+  17
+❱ 18 return digest == received_digest
+  19
+Suggested fix: Use the 'hmac.compare_digest' function instead of the '=='' operator to reduce the
+vulnerability to timing attacks.
+  17
+❱ 18 return hmac.compare_digest(digest, received_digest)
+  19
+
+┏━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━┳━━━━━━━━━━━━━━━━━━━━━━┳━━━━━┓
+┃ Files analyzed        ┃   1 ┃ Lines analyzed       ┃  18 ┃
+┃ Files skipped         ┃   0 ┃                      ┃     ┃
+┣━━━━━━━━━━━━━━━━━━━━━━━╋━━━━━╋━━━━━━━━━━━━━━━━━━━━━━╋━━━━━┫
+┃ Errors                ┃   1 ┃                      ┃     ┃
+┃ Warnings              ┃   0 ┃                      ┃     ┃
+┃ Notes                 ┃   0 ┃                      ┃     ┃
+┗━━━━━━━━━━━━━━━━━━━━━━━┻━━━━━┻━━━━━━━━━━━━━━━━━━━━━━┻━━━━━┛
+```