Add zsh completion script

Refer <https://www.gnu.org/software/automake/manual/automake.html#Third_002dParty-Makefiles>, use install-exec

Makefile

@@ -9,9 +9,11 @@ prefix = /usr/local
 includedir = $(prefix)/include
 libdir = $(prefix)/lib
 confdir = $(prefix)/etc
+datadir = $(prefix)/share
 
 exec_prefix = $(prefix)
 bindir = $(exec_prefix)/bin
+zshcompdir = $(datadir)/zsh/site-functions
 
 SRCS = $(sort $(wildcard src/*.c))
 OBJS = $(SRCS:.c=.o)
@@ -46,7 +48,9 @@ CFLAGS_MAIN=-DLIB_DIR=\"$(libdir)\" -DINSTALL_PREFIX=\"$(prefix)\" -DDLL_NAME=\"
 all: $(ALL_LIBS) $(ALL_TOOLS)
 
 #install: $(ALL_LIBS:lib/%=$(DESTDIR)$(libdir)/%) $(DESTDIR)$(LDSO_PATHNAME)
-install:
+install: install-exec install-config install-zsh-completion
+
+install-exec:
 	install -d $(DESTDIR)/$(bindir) $(DESTDIR)/$(libdir) $(DESTDIR)/$(confdir) $(DESTDIR)/$(includedir)
 	install $(INSTALL_FLAGS) 755 $(ALL_TOOLS) $(DESTDIR)/$(bindir)/
 	install $(INSTALL_FLAGS) 644 $(ALL_LIBS) $(DESTDIR)/$(libdir)/
@@ -55,6 +59,10 @@ install-config:
 	install -d $(DESTDIR)/$(confdir)
 	install $(INSTALL_FLAGS) 644 src/proxychains.conf $(DESTDIR)/$(confdir)/
 
+install-zsh-completion:
+	install -d $(DESTDIR)/$(zshcompdir)
+	install $(INSTALL_FLAGS) 644 completions/zsh/_proxychains4 -t $(DESTDIR)/$(zshcompdir)
+
 clean:
 	rm -f $(ALL_LIBS)
 	rm -f $(ALL_TOOLS)
@@ -70,6 +78,6 @@ $(LDSO_PATHNAME): $(LOBJS)
 $(ALL_TOOLS): $(OBJS)
 	$(CC) src/main.o src/common.o -o $(PXCHAINS)
 
-.PHONY: all clean install install-config
+.PHONY: all clean install install-exec install-config install-zsh-completion
 
 -include $(DEPS)

completions/zsh/_proxychains4

@@ -0,0 +1,3 @@
+#compdef proxychains4
+
+_arguments -s -S '1: :{_command_names -e}' '*:: :_normal'