add example to collaborative github chapter

The example is about implementing a temperature conversion library in Python. I think this example was by Barbara in the code refinery lesson.

Create a git[hub|lab] repository with a README and a LICENSE explaining shortly what those files are about. Add the opponent as a collaborator on the project.

Start by Googling the correct conversion. Write a Python code that works but is obviously faulty.

```python
# file: temperature.py
def convert(t):
return (t - 32) * 5/9
```

Have the opponent write an issue. There are several things that could be raised:

- No docstring
- Not clear which direction we're converting

Solve the issue by creating a branch and editing the `temperature.py` file. However, leave some obvious flaw, as to create some dialogue in the PR.

Create a feature request for the inverse conversion (Celcius to Fahrenheit), assign the opponent. Meanwhile, add a function for converting between celcius and kelvin in the main branch. This will create a merge conflict that we can resolve before merging.