Add README

README.md

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+# HiddenApiRefinePlugin
+
+A Gradle plugin that improves the experience when developing Android apps, especially system tools, that use hidden APIs.
+
+## Background
+
+When developing system tools, it's impossible inevitable to use hidden APIs. There are two ways to use hidden APIs, the reflection way and the linking way. For some types of system tools, a large amount of hidden APIs is required, the reflection way is too inconvenient. So the linking way is commonly used in those projects.
+
+In short, the linking way is to create Java-only modules with stub classes and then `compileOnly` them in the main Android modules. This is the same as what Android SDK's `android.jar` does.
+
+However the linking way, or "the stub way", have some problems:
+
+1. "Bridge classes" is required if only some members of the class are hidden.
+2. Kotlin will try to link public classes from the stub module, `implementation` a second Java-only which `compileOnly` the stub module can workaround the problem.
+3. Interface implementation will be removed by R8 if the stub module is not `compileOnly` directly from the main module, this will cause problem 2.
+
+This plugin is to solve these problems.
+
+## What do this plugin do
+
+This plugin uses the Transform API of the Android Gradle Plugin to create a transform that removes specific prefixes from class names. So we can add a special prefix (e.g., `'$'`) to stub classes, and all the problems will be gone and the stub module does not need to be a Java-only module.
+
+## Usage
+
+Root project:
+
+```gradle
+buildscript {
+    repositories {
+        mavenCentral()
+    }
+    dependencies {
+        classpath 'dev.rikka.tools:hidden-api-refine:1.0.0'
+    }
+}
+```
+
+Module:
+
+```gradle
+plugins {
+    id('dev.rikka.tools.hidden-api-refine')
+}
+
+hiddenApiRefine {
+    // Prefix to remove, default is ['$']
+    refinePrefix = ['$']
+    // Print log, default is true
+    log = true
+}
+```