readme: add build instructions

Refs #69161

Change-Id: I3647b469ccea5b62a659b00ee8a9ff9c65294edc

README.md

-RingClient
-==========
+Ring Mac OSX
+**********
 
 This is the official Mac port of Ring.
 
+Requirements
+=============
+
+- Ring daemon
+- libRingClient (Qt5 version)
+- Qt5 Core
+- Cocoa framework
+
+Build instructions
+==================
+
+2. mkdir build && cd build
+
+3. export CMAKE_PREFIX_PATH=<dir_to_qt5>
+
+Now generate an Xcode project with CMake:
+4. cmake ../ -DCMAKE_INSTALL_PREFIX=<libringclient_install_path> -G Xcode
+5. open Ring.xcodeproj/
+6. Build and run it from Xcode. You can also generate the final Ring.app bundle.
+
+You can also build it from the command line:
+
+4. cmake ../ -DCMAKE_INSTALL_PREFIX=<libringclient_install_path>
+5. make
+6. open Ring.app/
+
+
+Debugging
+==================
+
+For now, the build type of the client is "Debug" by default, however it is
+useful to also have the debug symbols of libRingClient. To do this, specify this
+when compiling libRingClient with '-DCMAKE_BUILD_TYPE=Debug' in the cmake
+options.