Windows: Clarify installation directory layout.

Suggested by eabase. #1346

doc/install.html

@@ -241,6 +241,19 @@ absolute path names — all modules are loaded relative to the
 directory where <tt>luajit.exe</tt> is installed
 (see <tt>src/luaconf.h</tt>).
 </p>
+<p>
+The final directory layout should look like this:
+</p>
+<pre class="code">
+├── luajit.exe
+├── lua51.dll
+├── <- put your own classic Lua/C API modules (*.dll) here
+└── lua
+    ├── <- put your own Lua modules (*.lua) here
+    └── jit
+        ├── bc.lua
+        └── (etc …)
+</pre>
 
 <h2 id="cross">Cross-compiling LuaJIT</h2>
 <p>