doc: document android_create_apk() resource and asset copying.

doc/changelog.dox

@@ -1056,6 +1056,10 @@ See also:
 -   Fixed most remaining warnings on MSVC, in particular those related to
     "conversion from T to void * of greater size" (see
     [mosra/magnum#544](https://github.com/mosra/magnum/issues/544)).
+-   The @cb{.cmake} android_create_apk() @ce CMake function gained an ability
+    to copy resources and assets to the APK. See @ref platforms-android-apps-cmake "the corresponding Android platform documentation"
+    and [mosra/toolchains#10](https://github.com/mosra/toolchains/pull/10) for
+    more information
 
 @subsection changelog-latest-bugfixes Bug fixes
 

doc/platforms-android.dox

@@ -285,6 +285,22 @@ if(CMAKE_ANDROID_NDK)
 endif()
 @endcode
 
+Besides packing the main library, the function can also copy resources and
+assets:
+
+@code{.cmake}
+android_create_apk(<target> <manifest>
+    [RESOURCE_DIRECTORY <res>]
+    [ASSET_DIRECTORY <assets>])
+@endcode
+
+The optional `RESOURCE_DIRECTORY` and `ASSET_DIRECTORY` arguments take relative
+or absolute paths to directories containing resources (usually named `res/`)
+and assets (usually named `assets/`). Both options track file dependencies, so
+the APK gets repacked when any files in the directories change contents, are
+added or removed. CMake before 3.12 checks the directories only during CMake
+runs, on newer versions at every incremental build.
+
 @subsection platforms-android-apps-gradle Using Gradle
 
 Besides plain CMake and Gradle it's also possible to use the classic