Document how to install yamllint

doc/ale-yaml.txt

@@ -5,6 +5,25 @@ ALE YAML Integration                                         *ale-yaml-options*
 ===============================================================================
 yamllint                                                    *ale-yaml-yamllint*
 
+Website: https://github.com/adrienverge/yamllint
+
+
+Installation
+-------------------------------------------------------------------------------
+
+Install yamllint in your a virtualenv directory, locally, or globally: >
+
+  pip install yamllint # After activating virtualenv
+  pip install --user yamllint # Install to ~/.local/bin
+  sudo pip install yamllint # Install globally
+
+See |g:ale_virtualenv_dir_names| for configuring how ALE searches for
+virtualenv directories.
+
+
+Options
+-------------------------------------------------------------------------------
+
 g:ale_yaml_yamllint_executable                 *g:ale_yaml_yamllint_executable*
                                                *b:ale_yaml_yamllint_executable*
   Type: |String|