README.md edited

README.md

@@ -25,6 +25,38 @@ with most codes, supports refinement mask generation for RAMSES.
     
 - Requires FFTW (v2 or v3), GSL (and HDF5 for output for some codes)
 
+## Building MUSIC
+While we still supply the old Makefile, using CMake is now the preferred way of building. 
+CMake use out-of-source build, i.e. you create a build directory, and then configure the code using CMake. Inside the `music` directory, do
+```
+  mkdir build
+  cd build
+  ccmake ..
+  make -j
+```
+to configure the code (you will se a menu), and then start a parallel compilation. If CMake has trouble finding your FFTW or HDF5 installation,
+you can add hints as follows
+```
+  FFTW3_ROOT=<path> HDF5_ROOT=<path> ccmake ..
+```
+If you want to build on macOS, then it is strongly recommended to use GNU (or Intel) compilers instead of Apple's Clang. Install them e.g. via homebrew and then configure cmake to use them instead of the macOS default compiler via
+```
+  CC=gcc-9 CXX=g++-9 ccmake ..
+```
+This is necessary since Apple's compilers haven't supported OpenMP for years.
+
+
+## Running
+
+There is an example parameter file 'example.conf' in the main directory. Possible options are explained in it, it can be run
+as a simple argument, e.g. from within the build directory:
+
+```
+  ./MUSIC ../ics_example.conf
+```
+
+
+## Disclaimer
 
 This program is distributed in the hope that it will be useful, but 
 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
@@ -32,7 +64,7 @@ or FITNESS FOR A PARTICULAR PURPOSE. By downloading and using MUSIC, you
 agree to the LICENSE, distributed with the source code in a text 
 file of the same name.
 
-
+## References
 [1]: http://arxiv.org/abs/1103.6031
 [2]: https://groups.google.com/forum/#!forum/cosmo_music
 [3]: https://bitbucket.org/ohahn/music/downloads/MUSIC_Users_Guide.pdf