docs: add WIP note (README.md)

README.md

@@ -6,6 +6,12 @@
   </p>
 </div>
 
+# WIP Note 🚧
+
+This branch (`nixd-next`) is still WIP! Please see https://github.com/nix-community/nixd/issues/283 for the migration plan.
+
+The [main](https://github.com/nix-community/nixd/tree/main) branch contains stable nixd codes.
+
 ## About
 
 This is a Nix language server that directly uses (i.e., is linked with) the official Nix library (https://github.com/NixOS/nix).
@@ -82,44 +88,3 @@ We have tested some working & reproducible [editor environments](/nixd/docs/edit
 - [Configuration Examples](nixd/docs/examples)
 - [Developers' Manual](nixd/docs/dev.md) (internal design, contributing):
 - Project matrix room: https://matrix.to/#/#nixd:matrix.org
-
-## Project Structure
-
-```
-.
-├── default.nix
-├── flake.lock
-├── flake.nix
-├── LICENSE
-├── lspserver                          # The C++ library for writing LSP servers.
-├── meson.build
-├── nixd                               # Modularized nixd components, test suite, and tools (binary)
-│   ├── docs                           # Documentation
-│   ├── include                        # General header files
-│   ├── lib
-│   │   ├── AST                        # AST library for nix expressions, static analysis (rename, completion, location, range) & evaluation bindings.
-│   │   ├── Expr                       # Expressions library (single AST nodes) with name lookups, locations, ...
-│   │   ├── meson.build
-│   │   ├── Nix                        # Extension to NixOS/nix
-│   │   ├── Parser                     # Extension to the parser from NixOS/nix. with ranges support & error handling.
-│   │   ├── Server                     # The nixd server library with controller (the process interacting with clients) and multiple workers (option, eval).
-│   │   └── Support
-│   ├── meson.build
-│   ├── test                           # Library tests. (rarely used)
-│   └── tools
-│       ├── meson.build
-│       ├── nix-ast-dump               # Dump nix AST from the offical parser (NixOS/nix)
-│       │   ├── meson.build
-│       │   ├── nix-ast-dump.cpp
-│       │   └── test
-│       ├── nixd                       # The nixd binary (entry point)
-│       │   ├── meson.build
-│       │   ├── nixd.cpp
-│       │   └── test                   # The regression tests.
-│       └── nixd-ast-dump              # Dump the AST nodes parsed from the extended parser, check leaks & memory safety.
-│           ├── meson.build
-│           ├── nixd-ast-dump.cpp
-│           └── test
-└── README.md
-
-```