add a gem description

Author: GrantBirki

entitlements.gemspec

@@ -4,7 +4,7 @@ Gem::Specification.new do |s|
   s.name = "entitlements"
   s.version = File.read("VERSION").chomp
   s.summary = "git-managed LDAP group configurations"
-  s.description = ""
+  s.description = "The Ruby Gem that Powers Entitlements - GitHub's Identity and Access Management System"
   s.authors = ["GitHub, Inc. Security Ops"]
   s.email = "[email protected]"
   s.license = "MIT"