add save results location

[lemorage]

Resolves #42

[radlinskii]

IMHO to be really clear it should be something like:

flag indicating if results should be saved to a file  ( `~/.local/share/donkeytype/donkeytype-results.csv`  on Linux and MacOS, and `C:\Users\{Username}\AppData\Local\donkeytype\donkeytype-results.csv` on Windows)

also in README.md you could update the line:

To view the history of results in a bar chart you can run:

to:

By default `donkeytype` saves results of tests to `~/.local/share/donkeytype/donkeytype-results.csv`  on **Linux** and **MacOS**, and `C:\Users\{Username}\AppData\Local\donkeytype\donkeytype-results.csv` on **Windows**. To view the history of results in a bar chart you can run:

[lemorage]

@radlinskii Got it. I wanted to keep it short at first, but I'll try your way this time.