docs: rewrite documentation.

add: Nix and Snapcraft support.

docs/commands/project-commands.mdx

@@ -0,0 +1,28 @@
+---
+sidebar_label: Project commands (new, init)
+---
+
+# Project Commands
+
+## `dcr new <name>`
+
+Creates a new project with a standard structure and `dcr.toml`. The `name` argument is required.
+
+```bash
+dcr new my-app
+```
+
+Generates:
+- `dcr.toml` with basic fields
+- `src/main.c` with a `main` template
+
+## `dcr init`
+
+Initializes a DCR project in the current (empty) directory.
+
+```bash
+mkdir app && cd app
+dcr init
+```
+
+The project name is taken from the current directory name.