fix: update implementation plan link in documentation

Author: pelikhan

docs/src/content/docs/dev/index.md

@@ -18,7 +18,7 @@ The template are stored in a [markdown-ish, framework agnostic, template format]
 
 :::tip
 
-Use the [implementation plan]() with your Agent to reimplement PromptPex quickly.
+Use the [implementation plan](https://github.com/microsoft/promptpex/blob/dev/.github/instructions/implementation.instructions.md) with your Agent to reimplement PromptPex quickly.
 
 :::