docs: add action summary to README

[ImDevinC]

Summary

• Adds documentation to README describing the Counter action's functionality
• Helps users quickly understand what each action in the plugin can do

Changes

The README now includes:

• An "Actions" section that lists all available actions
• A one-sentence summary of the Counter action explaining its key features (increment on short press, subtract/reset on long press, with optional persistence and file export)