docs/readme: add project structure (#219)

README.md

@@ -78,13 +78,44 @@ And diagnostic:
 - [Developers' Manual](docs/dev.md) (internal design, contributing):
 - Project matrix room: https://matrix.to/#/#nixd:matrix.org
 
-## Tooling
-
-We provide some extra tools based on our codebase.
-
-### nix-ast-dump
-
-Used for dumping internal data structures in nix parser.
-
-Demo: [all-grammar.nix](tools/nix-ast-dump/test/all-grammar.nix)
-
+## Proejct Structure
+
+```
+.
+├── default.nix
+├── docs
+├── editors
+├── flake.lock
+├── flake.nix
+├── LICENSE
+├── lspserver # The C++ library for writing LSP servers.
+├── meson.build
+├── nixd # Modularized nixd components, test suite, and tools (binary)
+│ ├── 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
+
+```