Update README.md

Author: halx99

README.md

@@ -99,6 +99,8 @@ Open [APPENDIX.md](APPENDIX.md) for additional information and see [Milestones](
 See [windows workflow guide](https://github.com/axis-project/axis/issues/564)
 
 #### Android
+
+##### With Android Studio
   1. Install Android Studio 2021.1.1+
   2. When starting Android Studio for the first time, It will guide you to install the SDK and other tools, just install them
   3. Start Android and choose [Open an existing Android Studio Project] and select ```axis\tests\cpp-tests\proj.android```
@@ -109,6 +111,21 @@ See [windows workflow guide](https://github.com/axis-project/axis/issues/564)
      * CMake 3.10+  
   5. Wait for ```Gradle sync``` finish.
   6. Note: If you use non-sdk provided CMake edition, you will need to download ```ninja``` from https://github.com/ninja-build/ninja/releases, and copy ```ninja.exe``` to cmake's bin directory
+  
+##### Without Android Studio
+  1. Download command-tools from https://developer.android.com/studio#command-tools
+  2. Install Android devtools (for example in windows)
+  ```bat
+  # unzip command-tools at D:\dev\adt\
+  # Install android devtools
+  cd D:\dev\adt\
+  mkdir sdk
+  .\cmdline-tools\bin\sdkmanager.bat --verbose --sdk_root=D:\dev\adt\sdk "platform-tools" "cmdline-tools;latest" "platforms;android-33" "build-tools;30.0.3" "cmake;3.22.1" "ndk;23.2.8568313"
+  set ANDROID_HOME=D:\dev\adt\sdk
+  
+  # Goto xxx\proj.android
+  .\gradlew.bat assembleRelease -PPROP_BUILD_TYPE=cmake -PPROP_APP_ABI=arm64-v8a --parallel --info
+  ```
 
 #### iOS
   1. Ensure xcode12+ & [cmake3.21+](https://github.com/Kitware/CMake/releases) are installed, install cmake command line support: ```sudo "/Applications/CMake.app/Contents/bin/cmake-gui" --install```