systemd: correct README hash after bump to version 237

systemd-237 slightly changed the README, but the hash was not updated
leading to legal-info failing.  Fix it.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/systemd/systemd.hash

@@ -2,4 +2,4 @@
 sha256	c83dabbe1c9de6b9db1dafdb7e04140c7d0535705c68842f6c0768653ba4913c	systemd-237.tar.gz
 sha256	ab15fd526bd8dd18a9e77ebc139656bf4d33e97fc7238cd11bf60e2b9b8666c6	LICENSE.GPL2
 sha256	dc626520dcd53a22f727af3ee42c770e56c97a64fe3adb063799d8ab032fe551	LICENSE.LGPL2.1
-sha256	f6a739f5ee7f10df6467021066038297c0150ff680db9a4b9f60da53b11aa560	README
+sha256	9c7709aa401a41c4c3f33ea75c34ae5d5354d62c310c3391c2a5958952d8aadd	README