add clusterctl for developer doc

Author: fabriziopandini

docs/book/src/clusterctl/dev.md

@@ -1 +1,80 @@
-# Using clusterctl while developing cluster API
+# clusterctl for Developers
+
+This document describes how to use `clusterctl` during the development workflow.
+
+## Prerequisites
+
+* A Cluster API development setup (go, git, etc.)
+* A local clone of the Cluster API GitHub repository  
+* A local clone of the GitHub repositories for the providers you want to install
+
+## Getting started
+
+### Build clustertl
+
+From the root of the local copy of Cluster API, you can build the `clusterctl` binary by running:
+
+```shell
+make clusterctl
+```
+
+The output of the build is saved in the `bin/` folder; In order to use it you have to specify
+the full path, create an alias or copy it into a folder under your `$PATH`.
+
+### Create a clusterctl-settings.json file
+
+Next, create a `clusterctl-settings.json` file and place it in your local copy of Cluster API. Here is an example:
+
+```yaml
+{
+  "providers": [ "cluster-api", "kubeadm-bootstrap", "aws"],
+  "provider_repos": ["../cluster-api-provider-aws"]
+}
+```
+
+**enable_providers** (Array[]String, default=[]): A list of the providers to enable. See [available providers]() for more details.
+
+**provider_repos** (Array[]String, default=[]): A list of paths to all the providers you want to use. Each provider must have
+a `clusterctl-settings.json` file describing how to build the provider assets.
+
+## Run the local-overrides hack!
+
+You can now run the local-overrides hack from the root of the local copy of Cluster API:
+
+```shell
+cmd/clusterctl/hack/local-overrides.py
+```
+
+The script reads from the local repositories of the providers you want to install, builds the providers assets,
+and place them in a local override folder located under `$HOME/.cluster-api/overrides/`.
+Additionally, the command output provide you `clusterctl init` command with all the necessary flags.
+
+```shell
+clusterctl local overrides generated from local repositories for the cluster-api, kubeadm-bootstrap, aws providers.
+in order to use them, please run:
+
+clusterctl init  --core cluster-api:v0.3.0 --bootstrap kubeadm-bootstrap:v0.3.0 --infrastructure aws:v0.5.0
+```
+
+## Available providers 
+
+The following providers are currently defined in the script:
+
+* `cluster-api`
+* `kubeadm-bootstrap`
+* `kubeadm-controlplane`
+* `docker`
+
+More providers can be added by editing the `clusterctl-settings.json` in your local copy of Cluster API;
+please note that each `provider_repo` should have its own `clusterctl-settings.json` describing how to build the provider assets, e.g.
+
+```yaml
+{
+  "name": "aws",
+  "config": {
+    "componentsFile": "infrastructure-components.yaml",
+    "nextVersion": "v0.5.0",
+    "type": "InfrastructureProvider"
+  }
+}
+```