Add build instructions

README.md

@@ -1,2 +1,28 @@
 # AdaptiveBrightness
 
+## Build instructions
+
+### Build on windows
+
+#### Prerequisites
+
+- Visual Studio 2019
+- Qt Visual Studio Tools
+- Qt Library
+
+#### Build steps
+
+Open the `sln` and build.
+
+### Build on linux
+
+#### Prerequisites
+
+Assumes Debian Buster: `sudo apt install qt5-default libqt5serialport5-dev`
+
+#### Build steps
+
+```console
+$ qmake CONFIG+=release # or CONFIG+=debug
+$ make
+```