shells/git-prompt.zsh: Add installation instructions in pkg-message

shells/git-prompt.zsh/Makefile

@@ -3,6 +3,7 @@
 PORTNAME=	git-prompt.zsh
 DISTVERSIONPREFIX=	v
 DISTVERSION=	2.1.0
+PORTREVISION=	1
 CATEGORIES=	shells
 
 MAINTAINER=	jrm@FreeBSD.org
@@ -19,10 +20,13 @@ GH_ACCOUNT=	woefe
 
 NO_ARCH=	yes
 NO_BUILD=	yes
-PLIST_FILES=	${DATADIR}/${PORTNAME}
+PLIST_FILES=	${DATADIR}/${PORTNAME} ${DOCSDIR}/README.md
+SUB_FILES=	pkg-message
 
 do-install:
 	@${MKDIR} ${STAGEDIR}${DATADIR}
 	${INSTALL_DATA} ${WRKSRC}/${PORTNAME} ${STAGEDIR}/${DATADIR}
+	@${MKDIR} ${STAGEDIR}${DOCSDIR}
+	${INSTALL_DATA} ${WRKSRC}/README.md ${STAGEDIR}/${DOCSDIR}
 
 .include <bsd.port.mk>

shells/git-prompt.zsh/files/pkg-message.in

@@ -0,0 +1,21 @@
+=============================================================
+
+To add the git status indicator to your prompt, source
+git-prompt.zsh in one of your Zsh startup files using
+
+source %%DATADIR%%${PORTNAME}/${PORTNAME}
+
+Next, add ' $(gitprompt)%# ' to the end of the PROMPT value
+like in the example below.
+
+PROMPT='%n@%m %~ $(gitprompt)%# '
+
+For details, refer to
+
+%%DOCSDIR%%/README.md
+
+or
+
+https://github.com/woefe/git-prompt.zsh
+
+=============================================================