add Makefile convenience wrapper, document it in README

README.md

@@ -87,6 +87,27 @@ tweak a knob the preset name updates to the closest match.
   connection (or `git`) on the first configure. To build against a local checkout
   instead, pass `-DJUCE_ROOT=/path/to/juce`.
 
+### Quick start (any platform)
+
+A `Makefile` is included as a convenience wrapper around the CMake commands
+below - it doesn't add any extra build logic, it just calls `cmake` for you:
+
+```sh
+make          # configure and build all formats (AU VST3 Standalone)
+make install  # build, then copy the plugins to the standard locations
+make clean    # remove the build directory
+```
+
+Pass CMake options straight through with `CMAKE_ARGS` (e.g.
+`make CMAKE_ARGS=-DJUCE_ROOT=/path/to/juce`), or override the defaults with
+`make BUILD_TYPE=Debug` or `make FORMATS="VST3 LV2"`. If you prefer to drive
+CMake directly, the underlying commands are:
+
+```sh
+cmake -B build -DCMAKE_BUILD_TYPE=Release -DMINDBALL_FORMATS="AU VST3 Standalone"
+cmake --build build -j --target Mindball_VST3 Mindball_AU Mindball_Standalone
+```
+
 ### macOS
 
 ```sh