adding rough docs

docs/src/getting-started/building-the-os.md

@@ -54,8 +54,6 @@ m
 
 ### Adding prebuilt binaries
 
-#### Emulator
-
 sync repo
 
 ```bash

docs/src/getting-started/rust-in-android.md

@@ -0,0 +1,136 @@
+# Rust In Android
+
+Because there are a lot of starknet libraries in rust, and the beerus client
+is written in rust, being able to run rust code on android is important
+for reaching MVP.
+
+The process for running a minimal rust "hello world" library on android is
+as follows:
+
+1. Get dependencies
+    - NDK
+        - https://github.com/bbqsrc/cargo-ndk
+        - cargo install cargo-ndk
+        - rustup target add x86_64-linux-android
+            - this is the only one we need although there are more
+        - install NDK from android studio as well
+        ![installing ndk](../assets/ndk-install.png)
+1. Update Cargo.toml
+```
+[lib]
+crate-type = ["cdylib"]
+```
+
+```
+[dependencies]
+jni = "0.21.1"
+```
+1. Write Java side
+
+```
+package com.example.rust_example;
+
+public class RustLib {
+
+    // define the interface for using the rust library below
+    public static native String hello(String input);
+
+    static {
+        // here we load the rust library we created
+        System.loadLibrary("example_rust_project");
+    }
+}
+```
+
+1. Write rust side (Use javac to compile C headers for reference)
+
+
+Use javac to compile the Java class into a C header.
+```bash
+javac
+```
+
+```
+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class com_example_rust_example_RustLib */
+
+#ifndef _Included_com_example_rust_example_RustLib
+#define _Included_com_example_rust_example_RustLib
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     com_example_rust_example_RustLib
+ * Method:    hello
+ * Signature: (Ljava/lang/String;)Ljava/lang/String;
+ */
+JNIEXPORT jstring JNICALL Java_com_example_rust_1example_RustLib_hello
+  (JNIEnv *, jclass, jstring);
+
+#ifdef __cplusplus
+}
+#endif
+#endif
+```
+
+Now we implement this C header in rust.
+```
+use jni::{
+    objects::{JClass, JString},
+    sys::jstring,
+    JNIEnv,
+};
+
+use super::hello;
+
+#[no_mangle]
+pub extern "C" fn Java_com_example_rust_1example_RustLib_hello<'local>(
+    mut env: JNIEnv<'local>, // this is the class that owns our static method
+    _class: JClass<'local>,
+    input: JString<'local>,
+) -> jstring {
+    // getting the input string from our android app out of java
+    let input: String = env
+        .get_string(&input)
+        .expect("Couldn't get java string!")
+        .into();
+
+    // creating a new java string to return to our android app
+    let output = env
+        .new_string(hello(&input))
+        .expect("Couldn't create a java string!");
+
+    output.into_raw()
+}
+```
+
+1. Build for android
+
+Run
+```
+make build-android
+```
+
+Copy the .so file to jni directory in android app.
+
+Use the library like any other library.
+
+```
+package com.example.rust_example
+
+import androidx.appcompat.app.AppCompatActivity
+import android.os.Bundle
+
+
+class MainActivity : AppCompatActivity() {
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_main)
+
+        val result = RustLib.hello("TEST")
+        println(result)
+    }
+}
+```