Merge branch 'update-install' into 'master'

README: ppa only works for Ubuntu based systems

See merge request !58

diff --cc README
index 83f6af2621e0e19bccbebca0a806ee77dd15447d,c1d8c7dea704907af10c985bd8efe16e30b144c7..c22523c5138bea436087cca2a63bb32a4f4605c9
--- 1/README
--- 2/README
+++ b/README
@@@ -15,15 -15,9 +15,15 @@@ Alternatively, visit [https://f-droid.o
  Installing
  ----------
  
- The easiest way to install the `fdroidserver` tools is on Debian, Ubuntu, Mint
- or other Debian based distributions, you can install using:
+ The easiest way to install the `fdroidserver` tools is on Ubuntu, Mint or other
+ Ubuntu based distributions, you can install using:
  
 +    sudo apt-get install fdroidserver
 +
 +For older Ubuntu releases or to get the latest version, you can get
 +`fdroidserver` from the Guardian Project PPA (the signing key
 +fingerprint is `6B80 A842 07B3 0AC9 DEE2 35FE F50E ADDD 2234 F563`)
 +
      sudo add-apt-repository ppa:guardianproject/ppa
      sudo apt-get update
      sudo apt-get install fdroidserver