Development: reduce the number of files watched by `nodemon`

In theory, `nodemon` should watch only 779,

```
root@716db483de08:/usr/src/app/checkouts/readthedocs.org# find ./readthedocs -type f -name '*.py' | wc -l
779
```

but it says it's watching ~5k:

```
web_1       | [nodemon] watching 4989 files
```

Related #160 