Add go version requirement

Signed-off-by: zhouhao <[email protected]>

Author: zhouhao

Makefile

@@ -1,5 +1,3 @@
-GO15VENDOREXPERIMENT=1
-export GO15VENDOREXPERIMENT
 PREFIX ?= $(DESTDIR)/usr
 BINDIR ?= $(DESTDIR)/usr/bin
 

README.md

@@ -1,6 +1,7 @@
 # oci-image-tool [![Build Status](https://travis-ci.org/opencontainers/image-tools.svg?branch=master)](https://travis-ci.org/opencontainers/image-tools)
 
 `oci-image-tool` is a collection of tools for working with the [OCI image format specification](https://github.com/opencontainers/image-spec).
+To build from source code, image-tools requires Go 1.7.x or above.
 
 ## Install