Add Omarchy Power Manager to README

[onlyVishesh]

Description

Adding OMarchy Power Manager, a powerful new battery controller and advanced sleep state manager that entirely replaces the default power plugin.

Type of Contribution

• New resource (theme, tool, tutorial, etc.)
• Update existing entry
• Fix broken link
• Improve documentation
• Other (please specify)

Resource Details

• Resource Name: OMarchy Power Manager
• Category: Plugins
• Link: https://github.com/onlyVishesh/omarchy-power-manager
• Description: Advanced battery controller with dynamic profile switching, smart
  thresholds, and native hibernation support.

Checklist

• I have read the Contributing Guidelines

• I have tested all links and they work

• The resource is relevant to Omarchy

• The description is clear and concise

• I have followed the formatting guidelines

• I have added the resource to the appropriate section

• I have maintained alphabetical order within the section

• The resource meets the quality standards outlined in CONTRIBUTING.md

  Additional Notes

  The repository has passed the 5-star requirement and the description meets the single- sentence standard ending with a period.