[ci skip] Advertise ViaLoader in README file (ViaVersion#3966)

Author: FlorianMichael

README.md

@@ -70,6 +70,8 @@ dependencies {
 If you need access to the existing protocol or platform implementations, use the parent artifact `viaversion`.
 Please note the [differences in licensing](#license).
 
+Note: If you want to make your own platform implementation of ViaVersion (and additional addons),
+you can use the [ViaLoader](https://github.com/ViaVersion/ViaLoader) project.
 
 Building
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