how-to-build.md

+## How to build the app on Ubuntu 18.04
+
+- Clone repository and select branch fairchat-master (or mergeWith1.n.n)
+    ```bash
+    $ git clone git@git.fairkom.net:chat/fairchat.ReactNative.git
+    $ cd fairchat.ReactNative
+    $ git checkout fairchat-master
+    ```
+(or checkout the branch with latest merge from upstream Rocket.Chat-ReactNative)
+
+- Install OpenJDK 8 (version 11 may have problems as some libraries are [deprecated](https://stackoverflow.com/questions/55735400/how-to-fix-java-lang-module-findexception-module-java-se-ee-not-found-error-w) like java.se.ee) and check if both java and javac are the same version 8
+
+- Install Android Studio custom set-up with checkboxes on for:
+>     Android SDK
+>     Android SDK Platform
+>     Android Virtual Device
+(see also https://facebook.github.io/react-native/docs/getting-started.html#android-development-environment )
+
+    ```bash
+    export ANDROID_HOME=~/Software/AndroidSDK
+    ```
+
+- Install dependencies from working dir and be sure to have a stable node version (10.13 or higher, not 8)
+    ```bash
+    $ sudo apt install nodejs npm curl
+    $ sudo npm cache clean -f
+    $ sudo npm install -g n
+    $ sudo n stable
+    $ sudo npm install -g yarn
+    $ sudo npm install -g react-native-cli 
+    $ sudo chown -R $USER:$(id -gn $USER) /home/ras/.config 
+    $ yarn global add react-native-cli
+    $ yarn config set cache-folder /media/someGBstorage/yarn/cache/
+    $ yarn
+    
+- forward 8081 ports if device is connected via USB (or change dev settings in device to connect via same WIFI to port 8081 on pc)
+
+    ```bash
+    $ adb reverse tcp:8081 tcp:8081
+    ```
+
+- Run Metro handler on port 8081 in separate terminal window in same working dir 
+
+    ```bash
+    $ npm start
+    ```
+
+- Build and run application
+    ```bash
+    $ react-native run-ios
+    ```
+    ```bash
+    $ react-native run-android
+    ```
+
+- Changing branch or merging commits requires full rebuild (react-native should not require this ...)
+
+```bash
+   $ git checkout newfeature
+   $ yarn 
+   $ react-native run-android
+```
+- You may also need to rebuild the storybook, which is checked with pre-commit (or do a `git clean` to remove the commit syntax checking)
+
+```bash
+yarn add --dev jest
+yarn global add jest
+jest --updateSnapshot
+```