Added installation documentation

website/src/posts/getting-started/posts/installation.md

@@ -0,0 +1,25 @@
+---
+title: "Installation"
+summary: ""
+eleventyNavigation:
+  key: Installation
+  parent: Getting Started
+  order: 2
+---
+
+Mappie is a Kotlin compiler plugin. The most convenient way to use compiler plugins is
+to apply the Gradle plugin which in term applies the compiler plugin to the Kotlin compilation.
+
+This can be achieved by adding the following snippet to the `build.gradle.kts` file.
+```kotlin
+plugins {
+    id("io.github.mappie") version "x.y.z"
+}
+```
+The `mappie-api` dependency must be added to the `build.gradle.kts` file for the programming interface
+```kotlin
+dependencies {
+    implementation("io.github.mappie:mappie-api:x.y.z")
+}
+```
+The most recent version of Mappie can be found at the [releases](https://github.com/Mr-Mappie/mappie/releases) page.