Update minimal required Android SDK version

Signed-off-by: Yevhen Babiichuk (DustDFG) <dfgdust@gmail.com>

docs/README-android.md

@@ -13,7 +13,7 @@ supported, but you can use the "android-project-ant" directory as a template.
 Requirements
 ================================================================================
 
-Android SDK (version 26 or later)
+Android SDK (version 31 or later)
 https://developer.android.com/sdk/index.html
 
 Android NDK r15c or later