docs: recommend rsdk instead

Signed-off-by: ZHANG Yuntian <[email protected]>

README.md

@@ -2,12 +2,11 @@
 
 [![Build](https://github.com/radxa-repo/rbuild/actions/workflows/build.yaml/badge.svg?branch=main)](https://github.com/radxa-repo/rbuild/actions/workflows/build.yaml)
 
-`rbuild` is our latest system image generator, which will replace our existing system build tool [`debos-radxa`](https://github.com/radxa/debos-radxa) soon.
-While both tools uses [`debos`](https://github.com/go-debos/debos) underneath, `rbuild` aims to fix many issues that was in `debos-radxa`:
-* Unable to generate custom image with different options due to hardcoded config files
-* Many duplicated/similar files in board support packages
-* Uses in-repo packages instead from an online APT repo
-* Confusing per-board package selection
+After more than 2 years of development, we have grown beyond what `rbuild`'s underlying dependencies are capable of.
+We have switched to a [lower-level tool](https://github.com/bdrung/bdebstrap) and completely restructured the project.
+
+Please use [`rsdk`](https://github.com/RadxaOS-SDK/rsdk) for the new project, which is meant to be compatible with
+existing `rbuild` systems. `rbuild` is now in maintenance mode.
 
 ## Usage
 

docs/first_image.md

@@ -1,5 +1,13 @@
 # Build your first image
 
+## Migration notice
+
+After more than 2 years of development, we have grown beyond what `rbuild`'s underlying dependencies are capable of.
+We have switched to a [lower-level tool](https://github.com/bdrung/bdebstrap) and completely restructured the project.
+
+Please use [`rsdk`](https://github.com/RadxaOS-SDK/rsdk) for the new project, which is meant to be compatible with
+existing `rbuild` systems. `rbuild` is now in maintenance mode.
+
 ## Install dependencies
 
 Currently, due to our dependency on [`debos`](https://github.com/go-debos/debos/issues/363), we can only run `rbuild` on x86 based system. If you are building in a virtual machine, you need to [enable nested virtualization](https://github.com/radxa-repo/rbuild/issues/16#issuecomment-1534176754), as KVM is required for building the image.