If your idea is really big, maybe it's worth discussing before even starting to work on it. If that's the case, please just open a new issue.
Getting started with development is really easy: there's no build step, just a Bash script. It is located under the bin folder.
The other folder, share, contains the templates that the tool can generate. All the script really does is just copy these templates from that location to another.
There is also a Makefile, it is used to install/uninstall and to run the tests:
make test
Before submitting a PR, just make sure the tests are still passing. You may also want to write new ones to test your feature.
After you've opened a PR, Travis CI will run the tests for you. You can keep pushing more commits to your branch; Travis will keep testing your changes.
Please be patient while waiting for your PR to be reviewed. We may suggest some changes or improvements or alternatives.
Here's how it's currently tested on AppVeyor (PowerShell):
cmd.exe /c 'install.bat'
bash -c "./test.sh ./elm-new"
You don't have to run this. A new build will be triggered automatically when you'll open a pull request.