Doc: Update installing section

Packages are now also available in Debian and Ubuntu.

README.rst

@@ -38,20 +38,24 @@ Screenshot
 Installation
 ^^^^^^^^^^^^
 
-On Fedora / CentOS :
+On Fedora / CentOS:
 
 .. code:: bash
 
  sudo dnf install yamllint
 
-On Ubuntu:
+On Debian 9+ / Ubuntu 16.04+:
 
 .. code:: bash
 
- sudo add-apt-repository -y ppa:adrienverge/ppa && sudo apt-get update
  sudo apt-get install yamllint
 
-On Debian: an official package is coming, it should be available soon.
+On older Debian / Ubuntu versions:
+
+.. code:: bash
+
+ sudo add-apt-repository -y ppa:adrienverge/ppa && sudo apt-get update
+ sudo apt-get install yamllint
 
 Alternatively using pip, the Python package manager:
 

docs/quickstart.rst

@@ -4,20 +4,24 @@ Quickstart
 Installing yamllint
 -------------------
 
-On Fedora / CentOS :
+On Fedora / CentOS:
 
 .. code:: bash
 
  sudo dnf install yamllint
 
-On Ubuntu:
+On Debian 9+ / Ubuntu 16.04+:
 
 .. code:: bash
 
- sudo add-apt-repository -y ppa:adrienverge/ppa && sudo apt-get update
  sudo apt-get install yamllint
 
-On Debian: an official package is coming, it should be available soon.
+On older Debian / Ubuntu versions:
+
+.. code:: bash
+
+ sudo add-apt-repository -y ppa:adrienverge/ppa && sudo apt-get update
+ sudo apt-get install yamllint
 
 Alternatively using pip, the Python package manager: