Spell out EL when defining EPEL

Author: aneta-petrova

guides/common/modules/ref_operating-system-requirements.adoc

@@ -22,7 +22,7 @@ endif::[]
 |====
 
 ifdef::foreman-el,katello,orcharhino[]
-Installing {Project} on a system with Extra Packages for {EL} (EPEL) is not supported.
+Installing {Project} on a system with Extra Packages for Enterprise Linux (EPEL) is not supported.
 endif::[]
 
 ifdef::satellite[]

guides/common/modules/ref_system-requirements-quickstart.adoc

@@ -22,7 +22,7 @@ endif::[]
 |====
 
 ifdef::foreman-el,katello,orcharhino[]
-Installing {Project} on a system with Extra Packages for {EL} (EPEL) is not supported.
+Installing {Project} on a system with Extra Packages for Enterprise Linux (EPEL) is not supported.
 endif::[]
 
 The installation requires {project-minimum-memory} of memory.