Create config file from default if not found

Similarly to pypsa-eur, the config file is not found, we create it as
a copy of `config.default.yaml`. This also makes it easier to include
pypsa-eur-sec as a subworkflow in a snakemake workflow.

Snakefile

@@ -1,7 +1,13 @@
 
+from os.path import exists
+from shutil import copyfile
+
 from snakemake.remote.HTTP import RemoteProvider as HTTPRemoteProvider
 HTTP = HTTPRemoteProvider()
 
+if not exists("config.yaml"):
+    copyfile("config.default.yaml", "config.yaml")
+
 configfile: "config.yaml"