doc: Add third party tools page

Closes lxc#556

Signed-off-by: Stéphane Graber <stgraber@stgraber.org>

doc/external_resources.md

@@ -5,4 +5,5 @@
 
 Project repository <https://github.com/lxc/incus>
 Image server <https://images.linuxcontainers.org>
+Third party tools </third_party>
 ```

doc/third_party.md

@@ -0,0 +1,35 @@
+# Third party tools and integrations
+Below are a list of common operations tools which feature Incus support, either natively or through a plugin.
+
+## Terraform / OpenTofu
+[Terraform](https://www.terraform.io) and [OpenTofu](https://opentofu.org) are infrastructure as code tools which focus on creating the infrastructure itself.
+For Incus, this means the ability to create projects, profiles, networks, storage volumes and of course instances.
+
+In most cases, one will then use Ansible to deploy the workloads
+themselves once the instances and everything else they need as been put in place.
+
+The integration with Incus is done through a [dedicated provider](https://github.com/lxc/terraform-provider-incus).
+
+## Ansible
+[Ansible](https://www.ansible.com) is an infrastructure as code tool with particular focus on software provisioning and configuration management.
+It does most of its work by first connecting to the system that it's deploying software on.
+
+To do that, it can connect over SSH and a variety of other protocols, one of which is [Incus](https://docs.ansible.com/ansible/latest/collections/community/general/incus_connection.html).
+
+That allows for easily deploying software inside of Incus instances without needing to first setup SSH.
+
+## Packer
+[Packer](https://www.packer.io) is a tool to generate custom OS images across a wide variety of platforms.
+
+A [plugin](https://developer.hashicorp.com/packer/integrations/bketelsen/incus) exists that allows Packer to generate Incus images directly.
+
+## Distrobuilder
+[Distrobuilder](https://github.com/lxc/distrobuilder) is an image building tool most known for producing the official LXC and Incus images.
+It consumes YAML definitions for its images and generates LXC container images as well as Incus container and VM images.
+
+The focus of Distrobuilder is in producing clean images from scratch, as opposed to repacking existing images.
+
+## GARM
+[GARM](https://github.com/cloudbase/garm) is the Github Actions Runner Manager which allows for running self-hosted Github runners.
+
+It supports a variety of providers for those runners, including [Incus](https://github.com/cloudbase/garm-provider-incus).