added documentation

api/README.md

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+## Repository
+
+To seamlessly integrate our API into your project, please visit
+our [repository](https://repo.thenextlvl.net/#/releases/net/thenextlvl/gopaint/api).
+Select your preferred build tool and incorporate the version you intend to use.
+
+### Gradle Example
+
+For Gradle users, add the repository and dependency to your `build.gradle.kts`:
+
+```kt
+repositories {
+    maven("https://repo.thenextlvl.net/releases")
+}
+
+dependencies {
+    compileOnly("net.thenextlvl.gopaint:api:version")
+}
+```
+
+> [!NOTE]
+> Be sure to replace `version` with the actual version number.<br>
+> The correct version of FastAsyncWorldEdit will be provided automatically<br>
+> Also you shouldn't shade the API into your Jar as it is already provided by the plugin.
+
+## API Documentation
+
+### The BrushController
+
+With the brush controller you can manage and retrieve brush settings from players and items
+
+```java
+BrushController controller = Bukkit.getServicesManager().load(BrushController.class);
+```
+
+### The BrushRegistry
+
+The brush registry allows you to register, unregister and retrieve brushes
+
+```java
+BrushRegistry registry = Bukkit.getServicesManager().load(BrushRegistry.class);
+```
+
+To register a new brush you have to invoke `BrushRegistry#register`
+
+### Creating new brushes
+
+In order to create a new brush you have to extend `Brush`,
+you need to provide a name, description and player head value.<br>
+In addition to that you have to overwrite the `Brush#paint` method.
+In there you perform all of your calculations and edits.<br>
+We recommend using `Brush#performEdit` to retrieve an edit session and `Brush#setBlock` to manipulate blocks,
+as it immediately frees resources after execution.
+
+For ease of use we provide some math classes for you:
+
+- Curve
+    - BezierSpline
+    - BezierSplineSegment
+- ConnectedBlocks
+- Height
+- Sphere
+- Surface
+
+> [!TIP]
+> You can always take a look at our default implementations of brushes if you need help
+