Update pnpm package manager reference in docs (#8288)

Add a reference link to pnpm package manager for an installation guide

Signed-off-by: Raghav Tengse <[email protected]>

Author: raghavexe

docs/getting-started.md

@@ -18,7 +18,7 @@ This guide will help you set up your development environment and make your first
 ## Prerequisites
 
 - Node.js (latest LTS version recommended)
-- pnpm package manager
+- [pnpm](https://pnpm.io/installation) package manager
 - Git
 - A GitHub account