readme: adding install info

After struggling a few hours on a machine with basically no stuff installed...
I discovered there were a few necessary things for the setup script to work :)
Merge pull request #48 from Leimi/patch-1

Readme: adding install info
User Google maps tiles instead of Mapbox example
Add generic key and update README
Merge pull request #49 from mainelabs/use-google-maps-tiles

User Google maps tiles instead of Mapbox example
fixing tiny english mistakes

je me faisais chier alors je me suis dit que
j'allais faire des trucs inutiles que seb kiff
adding tiny bits in the french locales/fixing punctuation

Oui vraiment, j'ai que ça à foutre.
translating in french the lonely and sad description placeholder