add installation instructions. prevent double-copy of licenses. skip build if targets are missing.

Builds/MacOSX/how to install.txt

@@ -0,0 +1,45 @@
+Release contains:
+
+```
+juicysfplugin.app        # standalone application, for playing around
+juicysfplugin.component  # AU plugin
+juicysfplugin.vst        # VST plugin
+juicysfplugin.vst3       # VST3 plugin
+```
+
+====
+
+To install plugins, move them to the following folder:
+
+```
+juicysfplugin.component -> ~/Library/Audio/Plug-Ins/Components/juicysfplugin.component
+juicysfplugin.vst       -> ~/Library/Audio/Plug-Ins/VST/juicysfplugin.vst
+juicysfplugin.vst3      -> ~/Library/Audio/Plug-Ins/VST3/juicysfplugin.vst3
+```
+
+If the folder `~/Library/Audio/Plug-Ins/VST` (or Components, or VST3) does not yet exist, make the folder yourself.
+
+A handy way to get to the folder `~/Library/Audio/Plug-Ins/` is to open Finder and use the "Go" keyboard shortcut:  
+⌘ + ⇧ + G
+
+====
+
+To install juicysfplugin.app, put it wherever you want (for example /Applications or ~/Applications).
+
+If you cannot open juicysfplugin.app, try _right-clicking_ it, and choose Open from the right-click menu. This gives you a _different dialogue_, with a new option, "Open".
+
+====
+
+Here's some soundfonts to get you started:
+
+- MuseScore's recommended soundfonts (includes MIT, GPL, other licenses)
+  - https://musescore.org/en/handbook/soundfonts-and-sfz-files#list
+- FlameStudios' guitar soundfonts (GPL-licensed)
+  - http://www.flamestudios.org/free/Soundfonts
+
+
+====
+
+Full instructions here:
+
+https://github.com/Birch-san/juicysfplugin/blob/master/README.md