[BUG] Documentation not complete or outdated

[leomrocha]

I'm currently following the README.md documentation and I've found a few issues that I'll enumerate here:

1. The first AirFlow DAG fails according to the airflow UI but there is a correct json output found on disk.

2. Using Aircan DAGs should redirect to a dataset already for the first test, it only names my-dataset but this is not enough to quickly have a running example, instead there is more complexity to find a dataset that can be used here.

3. In the GCP composer create should be added that the Image version is mandatory and there is no default for GCP, if no image version is given, the instance fails to start and is impossible to stop it.

4. On the GCP example, when asked to override the parameters, there is nothing there now
   Original image:
   

Now:

Even clicking EDIT does not give an option to override the params

5. Names an Example 2 but the examples are not enumerated.

6. For the same item, asks to add CKAN_SITE_URL and CKAN_SYSADMIN_API_KEY as Variables but first, there is no example 2 second what value should they contain?

Will add new items while I find them.

Also I will be updating the README.md for the things that I do find the solution by myself