Add basic documentation

Author: simonihmig

README.md

@@ -1,12 +1,18 @@
 ember-bootstrap-constraint-validations
 ==============================================================================
+[![CI](https://github.com/kaliber5/ember-bootstrap-constraint-validations/actions/workflows/ci.yml/badge.svg)](https://github.com/kaliber5/ember-bootstrap-constraint-validations/actions/workflows/ci.yml)
 
-[Short description of the addon.]
+This addon integration with [ember-bootstrap](https://www.ember-bootstrap.com/) to support form validations based on the
+browser's native HTML5 [constraint validation API](https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/Constraint_validation).
+But instead of the browser's built-in validation UI, validation errors will be rendered using Bootstrap's [Custom Styles](https://getbootstrap.com/docs/5.2/forms/validation/#custom-styles).
+See the [FormElement documentation](https://www.ember-bootstrap.com/api/classes/Components.FormElement.html) for
+further details.
 
 
 Compatibility
 ------------------------------------------------------------------------------
 
+* Ember Bootstrap v5 or above
 * Ember.js v3.24 or above
 * Ember CLI v3.24 or above
 * Node.js v12 or above
@@ -23,7 +29,28 @@ ember install ember-bootstrap-constraint-validations
 Usage
 ------------------------------------------------------------------------------
 
-[Longer description of how to use the addon in apps.]
+Apply the HTML5 validation attributes as needed to your form controls. The form elements [`@controlType`](https://www.ember-bootstrap.com/api/classes/Components.FormElement.html#property_controlType)
+argument will already apply the correct `type` attribute for the rendered `<input>` element. But you can also add 
+additional HTML5 attributes like `required`, by applying them as attributes to the form control. 
+For this you must use the block form syntax of form elements, so you can apply them to the yielded form `control` (which basically represents the `<input>`), 
+and not the parent *element* (a wrapper `<div>`):
+
+```hbs
+<BsForm @model={{this.model}} as |form|>
+  <form.element @label="Name" @property="name" as |el|>
+    <el.control required minlength="3"/>
+  </form.element>
+  <form.element @controlType="email" @label="Email" @property="email" />
+  <form.submitButton>Submit</form.submitButton>
+</BsForm>
+```
+
+In this example we have defined a "Name" text field, which is `required` and has a `minlength` of 3, as well as an optional field of type
+`email`. When submitting this form, or when focussing out of a field, the appropriate Bootstrap validation markup will be rendered:
+
+![validated form](./docs/validated-form.png)
+
+Note that the error messages are natively provided by the browser itself, given by the form element's [`validationMessage`](https://developer.mozilla.org/en-US/docs/Web/API/Constraint_validation#validationmessage).
 
 
 Contributing