Add ansible-lint and pip install to README

Prefer using the (python3) pip version of Ansible and ansible-lint so
that we can make use of recent Ansible features as needed.

Issue: INFRA-176
Change-Id: I80f1ac5cbe3b03201205c784217767a7fe903fc1
diff --git a/.gitignore b/.gitignore
index eea9339..0e1cef7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 *.retry
 *.log
 .vault_pass.txt
+.venv/
diff --git a/README.md b/README.md
index 0f46655..b42dee1 100644
--- a/README.md
+++ b/README.md
@@ -9,10 +9,20 @@
 
     $ git clone ssh://$USER@review.fairphone.software:29418/Infra/ansible-playbooks-secrets
 
-To use the playbooks install the `ansible` package:
+To use the playbooks install the `ansible` pip package.
 
-    $ sudo apt install ansible
+    $ virtualenv .venv/ansible -p python3
+    $ source .venv/ansible/bin/activate
+    $ pip3 install -r requirements.txt
 
+## Development
+
+Run the Ansible linter on changed playbooks before submitting patches. Besides
+basic validation checks, it also checks for best practices for Ansible playbook
+development.
+
+    $ pip3 install -r requirements-dev.txt
+    $ ansible-lint <playbook-name.yaml>
 
 ## Hiccup server proxy deployment
 
diff --git a/requirements-dev.txt b/requirements-dev.txt
new file mode 100644
index 0000000..81dc56b
--- /dev/null
+++ b/requirements-dev.txt
@@ -0,0 +1 @@
+ansible-lint~=4.1.0
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..bb304d2
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1 @@
+ansible~=2.7.9