Fix rm in Makefile and install LICENSE

Makefile

@@ -1,12 +1,15 @@
 PREFIX ?= /usr/local
 BINDIR = $(PREFIX)/bin
 MANDIR = $(PREFIX)/share/man
+LICENSEDIR = $(PREFIX)/share/licenses
 
 install:
 	# 755 is default
 	install -D -m 755 tdrop "$(DESTDIR)$(BINDIR)"
 	install -D -m 644 tdrop.groff "$(DESTDIR)$(MANDIR)"/man1/tdrop.1
+	install -D -m 644 LICENSE "$(DESTDIR)$($PREFIX)$(LICENSEDIR)"/tdrop/LICENSE
 
 uninstall:
 	rm -f "$(DESTDIR)$(BINDIR)"/tdrop
-	rf -rf "$(DESTDIR)$(MANDIR)"
+	rm -rf "$(DESTDIR)$(MANDIR)"
+	rm -rf "$(DESTDIR)$(LICENSEDIR)/tdrop"