docs: update readme

- clarify design goals
- mention scdoc dependency
- improve build command example

README.md

@@ -12,10 +12,11 @@ and missing features. If you run into a bug don't hesitate to
 
 - Simplicity and minimalism, river should not overstep the bounds of a
 window manger.
-- Dynamic window management based on a stack of views and tags like dwm.
-- Scriptable configuration and control through a separate binary,
-`riverctl`, like bspwm. This works using the custom
-[river-control](protocol/river-control-unstable-v1.xml) protocol.
+- Window management based on a stack of views and tags.
+- Dynamic layouts generated by external, user-written executables. (A default
+`rivertile` layout generator is provided.)
+- Scriptable configuration and control through a custom wayland protocol and
+separate `riverctl` binary implementing this protocol.
 
 ## Building
 
@@ -29,13 +30,15 @@ installed:
 - xkbcommon
 - pixman
 - pkg-config
+- scdoc (optional, but required for man page generation)
 
 *Note: NixOS users should refer to the
 [Building on NixOS wiki page](https://github.com/ifreund/river/wiki/Building-on-NixOS)*
 
 Then run, for example,
 ```
-sudo zig build -Drelease-safe=true --prefix /usr/local install
+zig build -Drelease-safe=true
+sudo zig build --prefix /usr/local install
 ```
 to build and install the `river` and `riverctl` binaries to
 `/usr/local/bin`. To enable experimental Xwayland support pass the