Slightly enhance documentation w.r.t suggestions given

This basically does the 3 following things:
- Adds `# :nodoc:` for the three modules that doesn't need any
  documentation. Thanks to Antonio for this suggestion.
- It replaces the link to `cop.rb` file as a permalink so it
  doesn't get broken over time. Thanks to David for this suggestion.
- Paraphrases a line in README.md so as to *not* use the word "cop"
  as readers might not be familiar with the term.

Signed-off-by: Utkarsh Gupta <utkarsh@debian.org>

README.md

@@ -3,9 +3,9 @@
 `RuboCop::Packaging` is an extension of [RuboCop](https://rubocop.org/),
 which is a Ruby static code analyzer (a.k.a. linter) and code formatter.
 
-It contains a set of Cops which enforces some of the guidelines that
-are expected of upstream maintainers so that the downstream can build
-their packages in a clean environment without any problems.  
+It helps enforcing some of the guidelines that are expected of upstream
+maintainers so that the downstream can build their packages in a clean
+environment without any problems.  
 Some of the other basic guidelines can be found
 [here](https://wiki.debian.org/Teams/Ruby/RubyExtras/UpstreamDevelopers).
 

docs/modules/ROOT/pages/index.adoc

@@ -3,8 +3,8 @@
 `RuboCop::Packaging` is an extension of [RuboCop](https://rubocop.org/),
 which is a Ruby static code analyzer (a.k.a. linter) and code formatter.
 
-It contains a set of Cops which enforces some of the guidelines that
-are expected of upstream maintainers so that the downstream can build
-their packages in a clean environment without any problems.
+It helps enforcing some of the guidelines that are expected of upstream
+maintainers so that the downstream can build their packages in a clean
+environment without any problems.  
 Some of the other basic guidelines can be found
 [here](https://wiki.debian.org/Teams/Ruby/RubyExtras/UpstreamDevelopers).

lib/rubocop/cop/packaging/gemspec_git.rb

@@ -1,11 +1,8 @@
 # frozen_string_literal: true
 
-# Rubocop module
-module RuboCop
-  # Cop module
-  module Cop
-    # Packaging module
-    module Packaging
+module RuboCop # :nodoc:
+  module Cop # :nodoc:
+    module Packaging # :nodoc:
       # This cop is used to identify the usage of `git ls-files`
       # and suggests to use a plain Ruby alternative, like `Dir`,
       # `Dir.glob` or `Rake::FileList` instead.
@@ -68,7 +65,7 @@ class GemspecGit < Cop
 
         # Extended from the Cop class.
         # More about the `#investigate` method can be found here:
-        # https://github.com/rubocop-hq/rubocop/blob/master/lib/rubocop/cop/cop.rb
+        # https://github.com/rubocop-hq/rubocop/blob/59543c8e2b66bff249de131fa9105f3eb11e9edb/lib/rubocop/cop/cop.rb#L13-L25
         #
         # Processing of the AST happens here.
         def investigate(processed_source)