Update URLs following name change OPFGenerator --> PGLearn.jl (#3)

- Update URLs following name change OPFGenerator --> PGLearn.jl (ad7f68dc18652bec68cc555c7354d4ca6040fab2)
- Update README.md (b5e1369511aa1245323da807fa254109d2ff89a2)


Co-authored-by: Mathieu Tanneau <mtanneau@users.noreply.huggingface.co>

README.md

@@ -93,8 +93,8 @@ and corresponding primal and dual solutions for the following OPF formulations
 * DC-OPF approximation (linear, convex)
 * Second-Order Cone (SOC) relaxation of AC-OPF (nonlinear, convex)
 
-This dataset was created using [OPFGenerator](https://github.com/AI4OPT/OPFGenerator);
-please see the [OPFGenerator documentation](https://ai4opt.github.io/OPFGenerator/dev/) for details on mathematical formulations.
+This dataset was created using [PGLearn.jl](https://github.com/AI4OPT/PGLearn.jl);
+please see the [PGLearn.jl documentation](https://ai4opt.github.io/PGLearn.jl/dev/) for details on mathematical formulations.
 
 ## Use cases