Add deprecation notice and link to alternative package (#9)

Added deprecation notice for the package.

Author: gdalle

README.md

@@ -1,5 +1,7 @@
 # WarcraftGridGraphs
 
+> This package is deprecated, please use [DecisionFocusedLearningBenchmarks.jl](https://github.com/JuliaDecisionFocusedLearning/DecisionFocusedLearningBenchmarks.jl).
+
 [![Build Status](https://github.com/gdalle/WarcraftGridGraphs.jl/actions/workflows/CI.yml/badge.svg?branch=main)](https://github.com/gdalle/WarcraftGridGraphs.jl/actions/workflows/CI.yml?query=branch%3Amain)
 [![Coverage](https://codecov.io/gh/gdalle/WarcraftGridGraphs.jl/branch/main/graph/badge.svg)](https://codecov.io/gh/gdalle/WarcraftGridGraphs.jl)