Merge pull request #736 from aniketsingh03/update-doc

[DOCS] Build details in README.md

README.md

+![Rocket.Chat logo](https://raw.githubusercontent.com/RocketChat/Rocket.Chat.Artwork/master/Logos/logo-dark.svg?sanitize=true)
+
 # Rocket.Chat Android native application
 
 [![CircleCI](https://circleci.com/gh/RocketChat/Rocket.Chat.Android/tree/develop.svg?style=shield)](https://circleci.com/gh/RocketChat/Rocket.Chat.Android/tree/develop) [![Build Status](https://travis-ci.org/RocketChat/Rocket.Chat.Android.svg?branch=develop)](https://travis-ci.org/RocketChat/Rocket.Chat.Android) [![Codacy Badge](https://api.codacy.com/project/badge/Grade/a81156a8682e4649994270d3670c3c83)](https://www.codacy.com/app/matheusjardimb/Rocket.Chat.Android) 
 
-# Get it from Google Play
-
-[![Rocket.Chat on Google Play](https://user-images.githubusercontent.com/551004/29770692-a20975c6-8bc6-11e7-8ab0-1cde275496e0.png)](https://play.google.com/store/apps/details?id=chat.rocket.android)
+## Description
+Currently, the app is maintained in two branches, namely `v1+` and `v2+`. The `v1+` is maintained in the `develop` branch and the `v2+` is maintained in the `develop-2.x` branch. The older version is written partially in `java` and `kotlin`, but we intend to write the latest version completely in `kotlin`.
 
+Clone the repository by running `git clone https://github.com/RocketChat/Rocket.Chat.Android.git` in your terminal. To build the v1.0+ of the app, run `git checkout develop` and to build the v2.0+, run `git checkout develop-2.x`. 
+Since both the versions use `kotlin` for some or all of their classes, following are the common prerequisites for both versions:
 ## How to build
-
-Retrolambda needs java8 to be installed on your system
+- Android Studio 3.0+ comes with built in kotlin support, so install the latest version (3.0+) of Android Studio (recommended). For older versions, you need to manually install kotlin plugin. Go to `File > Settings > Plugins` and search for `kotlin` and install it. You'll need to restart the IDE in order to see the changes.
+- Make sure that you have the latest **gradle** and the **android plugin** versions installed. Go to `File > Project Structure > Project` and make sure that you have the latest versions installed. Refer [this](https://developer.android.com/studio/releases/gradle-plugin.html#updating-gradle) to see the compatible versions.
+- Kotlin is already configured in the project. To check, go to `Tools > Kotlin > Configure Kotlin in project`. A message saying kotlin is already configured in the project pops up. You can update kotlin to the latest version by going to `Tools > Kotlin > Configure Kotlin updates` and download the latest version of kotlin.
+
+### Instructions specific to version
+#### v1.0+ 
+- After checking out to `develop` branch as mentioned above, simply import the project in Android Studio.
+
+#### v2+
+- This version requires the [Kotlin SDK](https://github.com/RocketChat/Rocket.Chat.Kotlin.SDK) for Rocket.Chat. Clone the Kotlin SDK in the **same directory** as the android repository by running `git clone https://github.com/RocketChat/Rocket.Chat.Kotlin.SDK.git`. Make sure that the android repository and the kotlin sdk have the same immediate parent directory.
+- First, a build is required for the SDK. Change your directory to the SDK directory by running `cd Rocket.Chat.Kotlin.SDK/` in your terminal. Any of the following approaches can be followed to successfully build the SDK.
+    - **Command Line** - (Within the kotlin SDK directory) Run `./gradlew clean && ./gradlew assemble` to successfully build the project.
+    - **Android Studio** - Import the project in Android Studio. Go to `Build > Make Project` to build the SDK successfully.
+After following the above methods, follow the following steps in your terminal window:
 ```
-export ANDROID_HOME=/path/to/android/sdk
-
-git clone https://github.com/RocketChat/Rocket.Chat.Android.git
-cd Rocket.Chat.Android
-
-echo "sdk.dir="$ANDROID_HOME > local.properties
-
-./gradlew assembleDebug
+cd ..
+cd Rocket.Chat.Android/app/libs
+ls
 ```
+Two `jar` files will be found in this directory (the `common` and `core` jar files), this indicates that the SDK was built correctly.
+- After the SDK has been built successfully, import the project in Android Studio and build it by following `Build > Make Project`.
+
+## How to run
+### Command Line
+- Connect your physical device to your pc via USB or start an emulator. Run `adb devices` in terminal. You should see your device in the list of devices.
+- In order to build the debug apk, run `./gradlew assembleDebug`. This would generate a debug apk which can be found under `Rocket.Chat.Android/app/build/outputs/apk/debug` folder with the name `app-debug.apk`.
+- In order to build and install the apk directly to the connected device, run `./gradlew installDebug`.
 
+### Android Studio
+- After importing the project in android studio, go to `Run > Run app` and then select your device, or create a new virtual device by following the wizard.     
 
 ## Bug report & Feature request
 
@@ -27,4 +47,4 @@ Please report via [GitHub issue](https://github.com/RocketChat/Rocket.Chat.Andro
 
 ## Coding Style
 
-Please follow our [coding style](https://github.com/RocketChat/Rocket.Chat.Android/blob/develop/CODING_STYLE.md) when contributing.
+Please follow our [coding style](https://github.com/RocketChat/java-code-styles/blob/master/CODING_STYLE.md) when contributing.