add readme

Author: Nathan Ho

README.md

@@ -0,0 +1,37 @@
+This is a minimal example of a SuperCollider server plugin. It compiles a "BoringMixer" ugen that takes the average of its two audio-rate inputs.
+
+## Compiling
+
+Make a directory for the `cmake` build files:
+
+```shell
+plugin-example/$ mkdir build && cd build
+plugin-example/build/$ cmake -DSC_PATH=/path/to/sc3source/ ..
+```
+
+If no `SC_PATH` is provided the build system assumes the SuperCollider include files in `/usr/include/SuperCollider/`.
+
+```shell
+plugin-example/build/$ make
+plugin-example/build/$ make install
+```
+
+On OSX, the plugins will end up in `sc3-plugins/build/SC3plugins`.
+
+WARNING: on OSX, if you want to install into `CMAKE_INSTALL_PREFIX`, you have to specify it by disabling the `IN_PLACE_BUILD` cmake option which defaults to ON (see below).
+
+## Installing
+
+Copy the `SC3plugins` folder to your Extensions folder. You can find out which one that is by evaluating
+
+```
+Platform.userExtensionDir
+```
+
+from within SuperCollider. Alternatively, you may install the extensions system-wide by copying to
+
+```
+Platform.systemExtensionDir
+```
+
+Tip: On OSX and Linux, it might be more convenient to use a symbolic link rather than copying or moving the directory.