Updated documentation with the new BUILDTOOLS_REVISION option

AddQtAndroidApk.cmake

@@ -68,6 +68,7 @@ include(CMakeParseArguments)
 #     VERSION_CODE 12
 #     PACKAGE_NAME "org.mycompany.myapp"
 #     PACKAGE_SOURCES ${CMAKE_CURRENT_LIST_DIR}/my-android-sources
+#     BUILDTOOLS_REVISION "23.0.3"
 #     KEYSTORE ${CMAKE_CURRENT_LIST_DIR}/mykey.keystore myalias
 #     KEYSTORE_PASSWORD xxxx
 #     DEPENDS a_linked_target "path/to/a_linked_library.so" ...

readme.md

@@ -142,6 +142,20 @@ add_qt_android_apk(my_app_apk my_app
 )
 ```
 
+### BUILDTOOLS_REVISION
+
+The revision of the Android SDK build tools. This must match a valid sub-folder of your <ANDROID_SDK>/build-tools directory. It seems like it can sometimes be needed, when the system cannot auto-detect it.
+
+Remains empty if not given.
+
+Example:
+
+```cmake
+add_qt_android_apk(my_app_apk my_app
+    BUILDTOOLS_REVISION "23.0.3"
+)
+```
+
 ### KEYSTORE
 
 The path to a keystore file and an alias, for signing the APK. If not provided, the APK won't be signed.