Add make install for linux

Makefile

@@ -2,6 +2,9 @@ CFLAGS?=-O2 -g -Wall -W
 CFLAGS+= -I./aisdecoder -I ./aisdecoder/lib -I./tcp_listener
 LDFLAGS+=-lpthread -lm
 
+ifeq ($(PREFIX),)
+    PREFIX := /usr/local
+endif
 UNAME := $(shell uname)
 ifeq ($(UNAME),Linux)
 #Conditional for Linux
@@ -60,3 +63,7 @@ $(EXECUTABLE): $(OBJECTS)
 
 clean:
 	rm -f $(OBJECTS) $(EXECUTABLE) $(EXECUTABLE).exe
+
+install:
+	install -d $(DESTDIR)$(PREFIX)/bin
+	install -m 755 $(DESTDIR)$(EXECUTABLE) "$(PREFIX)/bin/"

README

@@ -71,7 +71,7 @@ RTLSDR_LIB=$(RTLSDR_PATH)/build/src/
 -------  
 INSTALL
 -------
-On Linux, copy the rtl_ais file to a binary path, i.e.  /usr/bin, or /usr/local/bin. 
+On Linux, sudo make install
 On Windows, put the librtlsdr.dll and libusb-1.0.dll files in the same directory
 with rtl_ais.exe. You'll need the zadig driver installed too.