Adapt install instructions for OS X El Capitan

In El Capitan /usr/lib is not writable while /usr/lib/local is.

dcompiler.dd

@@ -171,7 +171,7 @@ $(H2 $(LNAME2 files, Files))
     )
 
     $(DT $(D $(DMDDIR)/osx/lib/$(LIB))
-    $(DD D runtime library (copy to $(D /usr/lib/$(LIB))))
+    $(DD D runtime library (copy to $(D /usr/local/lib/$(LIB))))
     )
     )
 
@@ -296,10 +296,10 @@ sudo cp $(DMDDIR)/osx/bin/dmdx.conf /usr/local/bin/$(DMD_CONF)
 )
     )
 
-    $(LI Copy the library to $(D /usr/lib):
+    $(LI Copy the library to $(D /usr/local/lib):
 
 $(CONSOLE
-sudo cp $(DMDDIR)/osx/lib/$(LIB) /usr/lib
+sudo cp $(DMDDIR)/osx/lib/$(LIB) /usr/local/lib
 )
     )
     )