Makefile: Use DESTDIR and PREFIX

Makefile

@@ -1,7 +1,9 @@
+PREFIX ?= /usr/local
+
 output: dwmblocks.c blocks.h
 	cc `pkg-config --cflags x11` `pkg-config --libs x11` dwmblocks.c -o dwmblocks
 clean:
 	rm -f *.o *.gch dwmblocks
 install: output
-	mkdir -p /usr/local/bin
-	cp -f dwmblocks /usr/local/bin
+	mkdir -p $(DESTDIR)$(PREFIX)/bin
+	cp -f dwmblocks $(DESTDIR)$(PREFIX)/bin