getting started guide: add a link to the available installation methods

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

docs/howto/getting-started.md

@@ -26,9 +26,7 @@ In this tutorial we explore the main features and concepts using the built-in we
 
 ## Installation
 
-You can easily install SFTPGo by downloading the appropriate package for your operating system and architecture. Please visit the [releases](https://github.com/drakkan/sftpgo/releases "releases") page.
-
-An official Docker image is available. Documentation is [here](./../../docker/README.md).
+You can easily install SFTPGo in several ways, more details [here](../../README.md#installation).
 
 In this guide, we assume that SFTPGo is already installed and running using the default configuration.