Add capability to build manpages from markdown

Adds capability to build the manpages via the go-md2man utility to the
make framework for containerd

Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com>

script/setup/install-dev-tools

@@ -8,3 +8,4 @@ go get -u github.com/stevvooe/protobuild
 go get -u github.com/alecthomas/gometalinter
 gometalinter --install >/dev/null
 go get -u github.com/LK4D4/vndr
+go get -u github.com/estesp/go-md2man