README: fix formatting

Add in some spaces that were inadvertently removed so that the mailing list
details aren't all squashed on one line.

Fixes: 763413e032cb ("README: add note on cross-compilation, miscellaneous improvements")
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
diff --git a/README.md b/README.md
index dc9e3fc..907b586 100644
--- a/README.md
+++ b/README.md
@@ -9,8 +9,8 @@
 Issues, Milestones, pull requests and code hosting is on GitHub:
 https://github.com/open-power/op-build
 
-Mailing list: openpower-firmware@lists.ozlabs.org
-Info/Subscribe: https://lists.ozlabs.org/listinfo/openpower-firmware
+Mailing list: openpower-firmware@lists.ozlabs.org  
+Info/Subscribe: https://lists.ozlabs.org/listinfo/openpower-firmware  
 Archives: https://lists.ozlabs.org/pipermail/openpower-firmware/
 
 ## Building an image