Add github template for using your own python run script (#4380)

Author: matt-gardner

README.md

@@ -38,8 +38,15 @@
 
 If you're interested in using AllenNLP for model development, we recommend you check out the
 [AllenNLP Guide](https://guide.allennlp.org).  When you're ready to start your project, we've
-created a template repository that you can use as a starting place:
-https://github.com/allenai/allennlp-template-config-files.
+created a couple of template repositories that you can use as a starting place:
+
+* If you want to use `allennlp train` and config files to specify experiments, use [this
+  template](https://github.com/allenai/allennlp-template-config-files). We recommend this approach.
+* If you'd prefer to use python code to configure your experiments and run your training loop, use
+  [this template](https://github.com/allenai/allennlp-template-python-script). There are a few
+  things that are currently a little harder in this setup (loading a saved model, and using
+  distributed training), but except for those its functionality is equivalent to the config files
+  setup.
 
 ## Package Overview