Add usage documentation

docs/usage.md

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+# Prefapp-Helm
+
+## Getting started
+
+In order to use prefapp-helm we need to include it as a subchart on our charts:
+
+```yaml
+# Chart.yaml
+
+dependencies:
+- name: prefapp-helm
+  version: 0.0.x  # the version We need/want
+  repository: https://prefapp.github.io/prefapp-helm
+```
+
+Then by updating our dependencies we are ready to go!
+
+```sh
+
+helm dep udpate . 
+
+```
+
+## Renders
+
+Prefapp-helm is a very lightweight microframework that exposes a reduced number of renders:
+
+* pod-render (ph.pod.render)
+* secret-render (ph.secret.render)
+* configmap-render (ph.configmap.render)
+* service-render (ph.service.render)
+* deployment-render (ph.deployment.render)
+* cronjob-render (ph.cronjob.render)
+* job-render (ph.job.render)
+* persistent-volume-render (ph.pv.render)
+* persistent-volume-claim-render (ph.pvc.render)
+
+
+Every render is just a [Helm named template](https://helm.sh/docs/chart_template_guide/named_templates/) that receives an object and renders it following the Kubernetes artifact definition.
+
+Therefore, if we use the configmap render:
+
+```yaml
+
+{{- define "my-configmap" -}}
+
+name: {{ .Release.Name}}
+
+# labels are optional
+
+data: 
+  a: value1
+  b: value2
+
+{{- end -}}
+
+{{/* render this object */}}
+{{ include "ph.configmap.render" (include "my-configmap" . | fromYaml ) }}
+
+```
+
+We obtain an expected [Configmap artifact](https://kubernetes.io/docs/concepts/configuration/configmap/) conformed to the api definition. 
+
+We can always let the definition of the key maps in the values section and pluck it to the configmap data section as so:
+
+```yaml
+
+---
+# values.yaml
+
+my_config:
+  a: value1
+  b: value2
+  # ...
+
+---
+# template/my-configmap.yaml
+
+{{- define "my-configmap" -}}
+
+name: {{ .Release.Name}}
+
+# labels are optional
+
+data:  {{ .Values.my_config | toYaml | nindent 2 }} # we pluck the section inside the data 
+
+{{- end -}}
+
+{{/* render this object */}}
+{{ include "ph.configmap.render" (include "my-configmap" . | fromYaml ) }}
+
+```
+
+
+
+
+
+
+
+
+
+
+
+
+
+```