Improving README (drastically)

Fixes #3

README.md

@@ -8,10 +8,99 @@ A Kirby v3 plugin for creating SVG donut (and pie) charts.
 This library is a Kirby v3 wrapper for the PHP port [`tiny-phpeanuts`](https://github.com/Fundevogel/tiny-phpeanuts) of the TypeScript library [`tiny-donuts`](https://github.com/Verivox/tiny-donuts).
 
 
+## How
+Install this package with [Composer](https://getcomposer.org):
+
+```text
+composer require fundevogel/kirby3-donuts
+```
+
+
+### Usage
+In order to generate a chart, we need some data first. The page method `toDonut()` accepts an array of data points as first argument - basically two or more arrays, each of which consists of `color` (string) and `value` (float):
+
+```php
+$data = [
+    ['color' => '#4F5D95', 'value' => 0.6],
+    ['color' => '#2b7489', 'value' => 0.4],
+];
+
+$page->doDonut($data);
+```
+
+There's also a field method `toDonut()` which takes `color` and `value` from a structure field. A basic example blueprint `fields/donut` (to be extended in your blueprint) looks like that:
+
+```yaml
+type: structure
+fields:
+  title:
+    label:
+      en: Title
+      de: Titel
+    type: text
+    width: 1/2
+
+  value:
+    label:
+      en: Value
+      de: Wert
+    type: number
+    min: 0
+    max: 1
+    step: .01
+    width: 1/4
+
+  color:
+    label:
+      en: Color
+      de: Farbe
+    type: text
+    width: 1/4
+```
+
+Both methods return a file object of the newly created SVG chart for further use.
+
+
+#### Options
+You may want to ..
+
+- change the thickness of the chart
+- the spacing between the segments
+- add classes to the output SVG element
+- make it a pie chart
+
+.. here's how:
+
+```php
+$page->doDonut($data, $thickness, $spacing, $classes, $isPieChart);
+```
+
+| Parameter     | Type   | Default   | Description                  |
+| ------------- | ------ | --------- | ---------------------------- |
+| `$data`       | array  | -         | data to be visualized        |
+| `$thickness`  | float  | see below | thickness of the chart       |
+| `$spacing`    | float  | see below | spacing between the segments |
+| `$classes`    | string | `''`      | classes applied to chart     |
+| `$isPieChart` | bool   | `false`   | make it a pie chart          |
+
+Attention: The field methods omits the `$data` argument (which is gathered from the structure field).
+
+
+#### Configuration
+You may also change certain options from your `config.php` globally (`'fundevogel.donuts.optionName'`):
+
+| Option        | Type   | Default   | Description                |
+| ------------- | ------ | --------- | -------------------------- |
+| `'thickness'` | float  | `3`       | global default thickness   |
+| `'spacing'`   | float  | `0.005`   | global default spacing     |
+| `'size'`      | int    | `100`     | `viewBox` width & height   |
+| `'inline'`    | bool   | `false`   | output inline SVG directly |
+| `'template'`  | string | `'donut'` | chart file template        |
+
+
 ## Roadmap
 - [ ] Add tests
-- [ ] Add pie charts
-- [ ] Add size adjustments
+
 
 ## Credits
 Naturally, a big shoutout goes to [Kim Almasan](https://github.com/Narquadah) & [Lars Krumbier](), who created `tiny-donuts` for [Verivox GmbH](https://github.com/Verivox). Most of the helper functions were taken from [Kirby](https://getkirby.com) by [Bastian Allgeier](https://github.com/bastianallgeier) (who's just awesome, btw).