03-packaging-installing: Improving episode.

Hi,

there are some things I'd suggest to improve Ep03:

### - Fix the ModuleNotFoundError

If I run the code in the current version of Episode 03, when I run the following line:

```
from conversions import temperature, speed
```

Assuming I'm in the `conversions/` directory as instructed, I get the following error:

```
---------------------------------------------------------------------------
ModuleNotFoundError Traceback (most recent call last)
in
----> 1 from conversions import temperature, speed

ModuleNotFoundError: No module named 'conversions'
```

This does work, if I'm in the `conversions/` directory:

```
from temperature import fahr_to_celsius
from speed import kph_to_ms
```

Not entirely sure if I am doing anything wrong.

If I open a Python terminal from the **parent directory of `conversions`** and run `import sys; sys.path.append('conversions')`, which is explained earlier in the episode, I can run the imports as they are currently displayed (`from conversions import temperature, speed`).

### - Move the Pip section to somewhere else in the Episode

As described in #58, the Pip section seems a bit out of place. I'd suggest moving it somewhere else in the Episode.

I will document other things I find in this issue. May I submit a PR to address these two points in the meantime?