Update install guide to include gitlab-ctl reconfigure prior to browsing

Why is this change being made?

When I followed the install guide to download and install Omnibus, it mentioned that the package automatically configures and starts GitLab, but it did not do this for RPM packages (tested on openSUSE 15.1, and CentOS 8). This changes the documentation to include an extra install_command instruction for RPM distro's, to run the reconfigure after installing the package. This way GitLab will be started before Step 3 which requires that GitLab is running.

The actual bug in the packaging should be addressed too, and then this patch reversed.

How will this merge request impact page speed?

Rather than have a separate "reconfigure" step, this MR adds one more install_command to the data file for the RPM distributions, to avoid extra lookups.

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what