Fix settings.example.py

Add some variables to settings.example.py that are expected throughout the code.

```
CWOD_HOME = "" # directory where data is downloaded, parsed, and ingested from
TMP_DIR = 'tmp/'
DB_PARAMS = ["localhost","username","password","capitolwords"]
DB_PATH = "" # path to api/capitolwords sqlite database
BIOGUIDE_LOOKUP_PATH = "" # path to api/bioguide_lookup.csv
```

I found that the code wouldn't run until these variables were at least defined. In addition, because these files are symlinked (as per the README) to the various subdirectories I couldn't come up with a single snippet of code that could properly set CWOD_HOME, DB_PATH, and BIOGUIDE_LOOK_PATH depending on where the file was being called referred to from. This is why I just left them as empty quotes and put a comment as to what it should be.