docs: document the command's starting directory

README.md

@@ -91,6 +91,8 @@ ecr [OPTIONS] <DISTRO[:VERSION]> [-- COMMAND...]
 | `--kernel[=PATH]` | Boot with QEMU system emulation. Downloads Alpine's default kernel if no `=PATH` given (`linux-virt`, or `linux-lts` on riscv64 where the virt flavor is not built) |
 | `-m, --memory <SIZE>` | Memory for QEMU VM (default: 2G, only with `--kernel`) |
 
+The command starts in the directory mapped from your current one: `/root/<name>` with the default `--bind`, `/mnt/<name>` with `--bind-rw`. With `--no-bind` (or when the current directory is not mapped) it starts in `/root`.
+
 ## Examples
 
 ```sh
@@ -101,6 +103,7 @@ ecr debian
 ecr alpine -- sh -c 'apk add curl && curl -s https://example.com'
 
 # Work on your project inside Ubuntu — changes are visible on the host
+# (the shell starts in /mnt/myapp, where the project is mounted)
 ecr ubuntu --bind-rw ~/projects/myapp
 
 # Native-compile for ARM64 through emulation (requires QEMU binfmt_misc)