howto install

Signed-off-by: Bruno Meilick <[email protected]>

readme.md

@@ -11,6 +11,14 @@ This plugin is free but if you use it in a commercial project please consider to
 - [buy me ☕](https://buymeacoff.ee/bnomei) or
 - [buy a Kirby license using this affiliate link](https://a.paddle.com/v2/click/1129/35731?link=1170)
 
+## Installation
+
+- for devkit-setup use `composer require bnomei/kirby3-thumb-imageoptim` or
+- extract latest release of [kirby3-thumb-imageoptim.zip](https://github.com/bnomei/kirby3-thumb-imageoptim/releases/download/v1.1.7/kirby3-thumb-imageoptim.zip) as folder `site/plugins/kirby3-thumb-imageoptim`
+
+> Installation as a gitsubmodule is *not* supported.
+
+
 ## Requirements
 
 - [ImageOptim API key](https://imageoptim.com/api/register) (trial available). This plugin uses v1.3.1.