Added a note about required regcode for elemental (#590) (#591)

Author: e-minguez

asciidoc/quickstart/elemental.adoc

@@ -255,12 +255,15 @@ operatingSystem:
   users:
     - username: root
       encryptedPassword: \$6\$jHugJNNd3HElGsUZ\$eodjVe4te5ps44SVcWshdfWizrP.xAyd71CVEXazBJ/.v799/WRCBXxfYmunlBO2yp1hm/zb4r8EmnrrNCF.P/
+  packages:
+    sccRegistrationCode: XXX
 EOF
 ----
 
 [NOTE]
 ====
 * The unencoded password is `eib`.
+* The `sccRegistrationCode` is needed to download and install the necessary RPMs from the official sources (alternatively, the `elemental-register` and `elemental-system-agent` RPMs can be manually side-loaded instead)
 * The `cat` command escapes each `$` with a backslash (`\`) so that Bash does not template them. Remove the backslashes if copying manually.
 * The installation device will be wiped during the installation.
 ====