wxmaxima: add a few caveats

Wxmaxima needs the standard caveat telling the user where the
app gets installed, plus one about linking the app, plus one
describing how to first setup wxmaxima to find maxima.

Fixes Homebrew/homebrew#15721

Closes Homebrew/homebrew#15790.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/wxmaxima.rb

@@ -18,4 +18,18 @@ class Wxmaxima < Formula
     prefix.install 'wxMaxima.app'
     system "make install"
   end
+
+  def caveats
+    <<-EOS.undent
+      The program you want to run is wxmaxima.app, and it gets installed into:
+        #{prefix}
+
+       To symlink it into Applications, you can type:
+         ln -s #{prefix}/wxmaxima.app /Applications
+
+       When you start wxmaxima the first time, you have to open Preferences,
+       and tell it where maxima is located.
+
+    EOS
+  end
 end