add example dag on project init

[andscoop]

• closes init command should create a “hello world” DAG in CLI #4

[schnie]

@andscoop what you think about breaking these files out into their own?

[andscoop]

We can - I thought above moving them to include/

[schnie]

Sounds good

[andscoop]

@schnie I broke the files out into /airflow/include. I originally planned to put them into /include/ but this would have potentially conflicted with the /include/ dir we create on astro airflow init if a developer is working from root astro directory.