config.default.yaml should be copied to config.yaml by new users.
That way config.yaml doesn't change every time the developers use new
settings.
A basic "Getting Started" section is added to the README.
Changes to be committed:
modified: .gitignore
modified: README.md
renamed: config.yaml -> config.default.yaml
Remove non-renewable generator and storage units from electricity-only
base network, since they're added differently here with links.
Remove unncessary cruft from config.yaml which is not used by
PyPSA-Eur-Sec (e.g. renewable configuration parameters).
Rename "naptha" to correct "naphtha".
