android: add some documentation

README.md

@@ -241,8 +241,31 @@ schroot --chroot jessie -- cmake --build build-in-chroot
 ```
 
 ## Android
+1. Set up [Android Studio/Android SDK](https://developer.android.com/studio).
 
-TODO
+### Android Studio
+Open the project located in the `android` folder and build.
+
+### Command-line
+```
+cd android
+./gradlew assembleRelease
+```
+
+### Customizing the build
+settings.gradle:
+* **rootProject.name** - project name displayed in Android Studio (optional).
+
+app/build.gradle:
+* **android->namespace** and **android->defaultConfig->applicationId** - set both to desired package name.
+* **getBuildNum** function - set **releaseDate** variable as desired.
+
+app/java/su/xash/hlsdk/MainActivity.java:
+* **.putExtra("gamedir", ...)** - set desired gamedir.
+
+src/main/AndroidManifest.xml:
+* **application->android:label** - set desired application name.
+* **su.xash.engine.gamedir** value - set to same as above.
 
 ## Nintendo Switch
 

android/app/build.gradle

@@ -12,7 +12,7 @@ android {
         applicationId 'com.example.hlsdk'
         versionName '1.0'
         versionCode getBuildNum()
-        minSdkVersion 19
+        minSdkVersion 3
         targetSdk 34
         compileSdk 34
     }
@@ -20,6 +20,7 @@ android {
     externalNativeBuild {
         cmake {
             version '3.22.1'
+            path file('../../CMakeLists.txt')
         }
     }
 
@@ -42,12 +43,6 @@ android {
         }
     }
 
-    externalNativeBuild {
-        cmake {
-            path file('../../CMakeLists.txt')
-        }
-    }
-
     lint {
         abortOnError false
     }

android/app/src/main/AndroidManifest.xml

@@ -13,7 +13,7 @@
             android:value="valve" />
 
         <activity
-            android:name=".MainActivity"
+            android:name="su.xash.hlsdk.MainActivity"
             android:exported="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />

android/app/src/main/java/su/xash/hlsdk/MainActivity.java

@@ -1,4 +1,4 @@
-package com.example.hlsdk;
+package su.xash.hlsdk;
 
 import android.app.Activity;
 import android.content.ComponentName;