Extendable base service for easier development.

docs/development.md

@@ -1,5 +1,7 @@
 # Development
 
+If you want to contribute to Homer, please read the [contributing guidelines](https://github.com/bastienwirtz/homer/blob/main/CONTRIBUTING.md) first. 
+
 ```sh
 # Using yarn (recommended)
 yarn install
@@ -10,6 +12,49 @@ npm install
 npm run serve
 ```
 
+## Custom services
+
+Custom services are small VueJs component (see `src/components/services/`) that add little features to a classic, "static", dashboard item. It should be very simple.
+A dashboard can contain a lot of items, so performance is very important. 
+
+The [`Generic`](https://github.com/bastienwirtz/homer/blob/main/src/components/services/Generic.vue) service provides a typical card layout which
+you can extend to add specific features. Unless you want a completely different design, extended the generic service is the recommended way. It gives you 3 [slots](https://vuejs.org/v2/guide/components-slots.html#Named-Slots) to extend: `icon`, `content` and `indicator`. 
+Each one is **optional**, and will display the usual information if omitted.
+
+Each service must implement the `item` [property](https://vuejs.org/v2/guide/components-props.html) and bind it the Generic component if used.
+
+### Skeleton
+```Vue
+<template>
+  <Generic :item="item">
+    <template #icon>
+      <!-- left area containing the icon -->
+    </template>
+    <template #content>
+      <!-- main area containing the title, subtitle, ... -->
+    </template>
+    <template #indicator>
+      <!-- top right area, empty by default -->
+    </template>
+  </Generic>
+</template>
+
+<script>
+import Generic from "./Generic.vue";
+
+export default {
+  name: "MyNewService",
+  props: {
+    item: Object,
+  },
+  components: {
+    Generic,
+  }
+};
+</script>
+```
+
+
 ## Themes
 
 Themes are meant to be simple customization (written in [scss](https://sass-lang.com/documentation/syntax)).