Add build guide

doc/BUILD.adoc

@@ -0,0 +1,53 @@
+= Build Zen from source
+
+If this is your first time to build Zen from source,
+we recommend that you build in the order described in this guide.
+
+== Install packages
+
+See the https://www.zwin.dev/getting_started/installation#install-packages[Install package]
+section of the general installation guide.
+These packages are what we need to build Zen.
+
+== Build & Install
+
+Use clang for build.
+
+```
+$ export CC=clang
+$ export CXX=clang++
+```
+
+=== Zwin
+
+See https://github.com/zwin-project/zwin#build--install[Build & Install] in Zwin README.
+
+=== Zen Mirror
+
+See https://github.com/zwin-project/zen-mirror/blob/main/doc/BUILD.adoc[Build Zen Mirror from source].
+
+=== zen-remote
+
+Instead of cloning zen-remote again, we recommend using zen-remote in
+the zen-mirror's git submodule: +
+`zen-mirror/app/3rdParty/zen-remote`.
+
+See https://github.com/zwin-project/zen-remote#build--install[Build & Install] in zen-remote README.
+
+=== Zukou
+
+See https://github.com/zwin-project/zukou#build--install[Build & Install] in Zukou README.
+
+=== Zennist
+
+See https://github.com/zwin-project/zennist#build--install[Build & Install] in Zennist README.
+
+=== Zen
+
+At project root,
+
+[source, shell]
+----
+$ meson build
+$ ninja -C build install
+----

doc/CONTRIBUTING.adoc

@@ -48,10 +48,10 @@ graph LR
 
 Zen consists primarily of the following repositories and libraries
 
-* https://wayland.freedesktop.org/[Wayland] +
+* https://wayland.freedesktop.org/[Wayland] (external library) +
 A base windowing system.
 
-* https://gitlab.freedesktop.org/wlroots/wlroots[wlroots] +
+* https://gitlab.freedesktop.org/wlroots/wlroots[wlroots] (external library) +
 A modular Wayland compositor library.
 
 * https://github.com/zwin-project/zwin[zwin] +
@@ -81,4 +81,6 @@ https://drive.google.com/file/d/1NoGWE1EHY5UVrd0lk0KV-sCUGy1w9xLJ/view?usp=shari
 
 == Build Zen from source
 
-TBD
+The first step in contributing to Zen by writing code is to build Zen from source.
+
+See link:./BUILD.adoc[BUILD.adoc].