doc: include short docs about bmake

doc/hooks/bmake.section.md

@@ -0,0 +1,7 @@
+# bmake {#bmake-hook}
+
+[bmake](https://www.crufty.net/help/sjg/bmake.html) is the portable variant of
+NetBSD make utility.
+
+In Nixpkgs, `bmake` comes with a hook that overrides the default build, check,
+install and dist phases.

doc/hooks/index.md

@@ -8,6 +8,7 @@ The stdenv built-in hooks are documented in [](#ssec-setup-hooks).
 autoconf.section.md
 automake.section.md
 autopatchelf.section.md
+bmake.section.md
 breakpoint.section.md
 cmake.section.md
 gdk-pixbuf.section.md