SPARK-1873: Add README.md file when making distributions

Author: Patrick Wendell <[email protected]>

Closes apache#818 from pwendell/reamde and squashes the following commits:

4020b11 [Patrick Wendell] SPARK-1873: Add README.md file when making distributions

Author: pwendell

make-distribution.sh

@@ -191,6 +191,7 @@ fi
 mkdir "$DISTDIR"/conf
 cp "$FWDIR"/conf/*.template "$DISTDIR"/conf
 cp "$FWDIR"/conf/slaves "$DISTDIR"/conf
+cp "$FWDIR/README.md" "$DISTDIR"
 cp -r "$FWDIR/bin" "$DISTDIR"
 cp -r "$FWDIR/python" "$DISTDIR"
 cp -r "$FWDIR/sbin" "$DISTDIR"