[Docs] Correct OS capitalization in the macOS validation example

## Location docs/installation.md, Requirements, macOS warning ## Problem The documented validation error says: DockSight installs on linux and windows, this host runs darwin`n The operating-system names are incorrectly lowercase and the sentence is missing normal punctuation. ## Correction Use consistent names and punctuation, for example: DockSight installs on Linux and Windows; this host runs Darwin. ## Acceptance criteria - The example uses Linux, Windows, and Darwin. - The sentence is grammatically correct. - No implementation or validation behavior is changed.