docs/manual: misc improvements to Vagrant usage documentation

* Changing back wget to curl cause wget it's not available
  on mac os x.
* Braking up too long windows one liner.

Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/getting.txt

@@ -19,13 +19,15 @@ If you want to setup an isolated buildroot environment on Linux or Mac
 Os X, paste this line onto your terminal:
 
 --------------------
-wget https://buildroot.org/downloads/Vagrantfile; vagrant up
+curl -O https://buildroot.org/downloads/Vagrantfile; vagrant up
 --------------------
 
 If you are on Windows, paste this into your powershell:
 
 --------------------
-(new-object System.Net.WebClient).DownloadFile("https://buildroot.org/downloads/Vagrantfile","Vagrantfile"); vagrant up
+(new-object System.Net.WebClient).DownloadFile(
+"https://buildroot.org/downloads/Vagrantfile","Vagrantfile");
+vagrant up
 --------------------
 
 If you want to follow development, you can use the daily snapshots or