README: add note about licenses of other components.

Author: greenrobot-team

README.md

@@ -183,3 +183,6 @@ Besides JVM based languages like Java and Kotlin, ObjectBox also offers:
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
+
+Note that this license applies to the code in this repository only.
+See our website on details about all [licenses for ObjectBox components](https://objectbox.io/faq/#license-pricing).