index.html: add "How to choose MXE target"

docs/index.html

@@ -128,6 +128,26 @@
         See the <a href="build-matrix.html">current status</a>
         for individual packages.
     </p>
+    <p>
+        How to choose MXE target:
+        <ol>
+            <li>if you want a 64 bit Windows executable,
+                statically linked into one big executable:
+                use MXE_TARGET x86_64-w64-mingw32.static;</li>
+            <li>if you want a 64 bit Windows executable,
+                splitted in an executable and dependant dlls
+                use MXE_TARGET x86_64-w64-mingw32.shared;</li>
+            <li>if you want a 32 bit Windows executable,
+                statically linked into one big executable:
+                use MXE_TARGET i686-w64-mingw32.static;</li>
+            <li>if you want a 32 bit Windows executable,
+                splitted in an executable and dependant dlls
+                use MXE_TARGET i686-w64-mingw32.shared.</li>
+        </ol>
+        Remark: the 'w64-mingw32' in those names are left-overs from
+        historical evolutions in the open source cross-compilation world
+        and refer in no way to the result being 64 or 32 bit Windows.
+    </p>
     <p>
         OpenMP (<a href="http://gcc.gnu.org/projects/gomp/">libgomp</a>)
         and pthreads (<a href="http://mingw-w64.sourceforge.net/">winpthreads</a>)