add pre-commit hook to facilitate local testing (#9158)

* add pre-commit hook configuration

* add tmp.md to .gitignore

* describe the use of pre-commit hook in CONTRIBUTING.md

* fix docs/integration.md errors identified by markdownlint

* fix docs/<file>.md errors identified by markdownlint

* docs/azure-csi.md
* docs/azure.md
* docs/bootstrap-os.md
* docs/calico.md
* docs/debian.md
* docs/fcos.md
* docs/vagrant.md
* docs/gcp-lb.md
* docs/kubernetes-apps/registry.md
* docs/setting-up-your-first-cluster.md
* docs/vagrant.md
* docs/vars.md

* fix contrib/<file>.md errors identified by markdownlint

docs/debian.md

@@ -3,34 +3,39 @@
 Debian Jessie installation Notes:
 
 - Add
-  
-  ```GRUB_CMDLINE_LINUX="cgroup_enable=memory swapaccount=1"```
-  
-  to /etc/default/grub. Then update with
-  
-  ```ShellSession
-   sudo update-grub
-   sudo update-grub2
-   sudo reboot
+
+  ```ini
+  GRUB_CMDLINE_LINUX="cgroup_enable=memory swapaccount=1"
   ```
-  
+
+  to `/etc/default/grub`. Then update with
+
+  ```ShellSession
+  sudo update-grub
+  sudo update-grub2
+  sudo reboot
+  ```
+
 - Add the [backports](https://backports.debian.org/Instructions/) which contain Systemd 2.30 and update Systemd.
-  
-  ```apt-get -t jessie-backports install systemd```
-  
+
+  ```ShellSession
+  apt-get -t jessie-backports install systemd
+  ```
+
   (Necessary because the default Systemd version (2.15) does not support the "Delegate" directive in service files)
-  
+
 - Add the Ansible repository and install Ansible to get a proper version
 
   ```ShellSession
   sudo add-apt-repository ppa:ansible/ansible
   sudo apt-get update
   sudo apt-get install ansible
-
   ```
 
 - Install Jinja2 and Python-Netaddr
 
-  ```sudo apt-get install python-jinja2=2.8-1~bpo8+1 python-netaddr```
-  
+  ```ShellSession
+  sudo apt-get install python-jinja2=2.8-1~bpo8+1 python-netaddr
+  ```
+
 Now you can continue with [Preparing your deployment](getting-started.md#starting-custom-deployment)