Added ansible script installation option

Signed-off-by: Lana Ivina <lana@ipdb.io>

docs/root/source/installation/network-setup/bigchaindb-node-ansible.md

@@ -0,0 +1,7 @@
+# Setting up a network of nodes with the Ansible script 
+
+You can find one of the installation methods with Ansible on GitHub at:
+
+[Ansible script](https://github.com/bigchaindb/bigchaindb-node-ansible)
+
+It allows to install BigchainDB, MongoDB, Tendermint, and python, and then connect nodes into a network. Current tested machine is Ubuntu 18.04. 

docs/root/source/installation/network-setup/index.rst

@@ -15,3 +15,5 @@ There are several ways to setup a network. You can use the Kubernetes deployment
    networks
    network-setup
    k8s-deployment-template/index
+   bigchain-node-ansible.md
+   

docs/root/source/installation/node-setup/bigchaindb-node-ansible.md

@@ -0,0 +1,7 @@
+# Setting up a network of nodes with the Ansible script 
+
+You can find one of the installation methods with Ansible on GitHub at:
+
+[Ansible script](https://github.com/bigchaindb/bigchaindb-node-ansible)
+
+It allows to install BigchainDB, MongoDB, Tendermint, and python, and then connect nodes into a network. Current tested machine is Ubuntu 18.04. 

docs/root/source/installation/node-setup/index.rst

@@ -15,6 +15,7 @@ You can use the all-in-one docker solution, or install Tendermint, MongoDB, and
    deploy-a-machine
    aws-setup
    all-in-one-bigchaindb
+   bigchaindb-node-ansible
    set-up-node-software
    set-up-nginx
    configuration