Add README.md to linux release tarballs

fix #8160

Author: hebasto

contrib/gitian-descriptors/gitian-linux.yml

@@ -184,6 +184,7 @@ script: |
     rm -rf ${DISTNAME}/lib/pkgconfig
     find ${DISTNAME}/bin -type f -executable -exec ../contrib/devtools/split-debug.sh {} {} {}.dbg \;
     find ${DISTNAME}/lib -type f -exec ../contrib/devtools/split-debug.sh {} {} {}.dbg \;
+    cp ../doc/README.md ${DISTNAME}/
     find ${DISTNAME} -not -name "*.dbg" | sort | tar --no-recursion --mode='u+rw,go+r-w,a+X' --owner=0 --group=0 -c -T - | gzip -9n > ${OUTDIR}/${DISTNAME}-${i}.tar.gz
     find ${DISTNAME} -name "*.dbg" | sort | tar --no-recursion --mode='u+rw,go+r-w,a+X' --owner=0 --group=0 -c -T - | gzip -9n > ${OUTDIR}/${DISTNAME}-${i}-debug.tar.gz
     cd ../../