test: add explanatory comments

test.gaybuild

@@ -1,26 +1,35 @@
+# the set keyword sets a property of the current scope
+# (i.e. the entire build script, a module, etc.)
 set RUSTC_EXE = "rustc";
 set ASM_EXE = "clang";
 set CC_EXE = "clang";
 set LINK_EXE = "ld.lld";
 set BUILD_PREFIX = "build";
 
+# a module is a single compile target.
+# modules can depend on other modules.
 module kern {
+    # the type keyword defines whether the module is supposed to be
+    # compiled into an executable binary (exe) or a library (lib).
     type exe;
+    # the depend keyword adds one or more dependencies to the module.
     depend [
         libk,
         arch,
     ];
+    # the source keyword adds one or more source files to the module.
+    # the file extension determines what language/compiler to use.
     source "kern/lib.rs";
 }
 
 module libk {
-    type static; # static library
+    type lib;
     depend arch;
     source "libk/lib.rs";
 }
 
 module arch {
-    type static;
+    type lib;
     source [
         "arch/lib.rs",
         "arch/**.nasm",