(CAT-1742) Update hiera README

Prior to this commit, the README.md file was not up to date with the
latest information on hiera usage.

This commit aims to update the README.md to ensure that users have
access to the correct information, based on our documentation.

README.md

@@ -888,66 +888,57 @@ end
 
 ## Hiera integration
 
-### Configuration
-
-Set the hiera config symbol properly in your spec files:
+At some point, you might want to make use of Hiera to bring in custom parameters for your class tests. In this section, we will
+provide you with basic guidance to setup Hiera implementation within rspec testing. For more information on Hiera, you should
+check our official [documentation](https://www.puppet.com/docs/puppet/8/hiera.html).
 
-```ruby
-let(:hiera_config) { 'spec/fixtures/hiera/hiera.yaml' }
-hiera = Hiera.new(:config => 'spec/fixtures/hiera/hiera.yaml')
-```
+### Configuration
 
-Create your spec hiera files
+The first step is to create the general hiera configuration file. Since we want this to be exclusive for testing, we recommend creating
+it inside your spec folder. Something along the lines of `spec/fixtures/hiera/hiera.yaml`. It should look something like this:
 
-spec/fixtures/hiera/hiera.yaml
-```ruby
+```yaml
 ---
-:backends:
-  - yaml
-:hierarchy:
-  - test
-:yaml:
-  :datadir: 'spec/fixtures/hiera'
+version: 5
+defaults:               # Used for any hierarchy level that omits these keys.
+  datadir: data         # This path is relative to hiera.yaml's directory.
+  data_hash: yaml_data  # Use the built-in YAML backend.
+
+hierarchy:
+  - name: 'rspec'
+    path: 'rspec-data.yaml'
 ```
 
-spec/fixtures/hiera/test.yaml
-```ruby
----
-ntpserver: ['ntp1.domain.com','ntpXX.domain.com']
-user:
-  oneuser:
-    shell: '/bin/bash'
-  twouser:
-    shell: '/sbin/nologin'
+It is often recommended to use dummy data during testing to avoid real values from being entangled. In order to create
+these values, we will need a new file containing this data exclusively, normally existing within a subfolder called `data`, ending up with
+`spec/fixtures/hiera/data/rspec-data.yaml`. Here is an example of its contents:
+
+```yaml
+ntpserver: 'ntp1.domain.com'
+user: 'guest'
+password: 'unsafepassword1'
 ```
 
-### Use hiera in your tests
+Finally, we make the target class spec file load the Hiera config, at which point we will be able to freely access it:
 
 ```ruby
-  ntpserver = hiera.lookup('ntpserver', nil, nil)
-  let(:params) { 'ntpserver' => ntpserver }
+let(:hiera_config) { 'spec/fixtures/hiera/hiera.yaml' }
 ```
+#### Enabling lookup()
 
-### Enabling hiera lookups
-If you just want to fetch values from hiera (e.g. because
-you're testing code that uses explicit hiera lookups) just specify
-the path to the hiera config in your `spec_helper.rb`
+There will also be situations in which you will simply want to fetch values from hiera across one or many testing files(e.g. because you're testing code 
+that uses explicit hiera lookups). In this case, just specify the path to the hiera config in your `spec_helper.rb`:
 
 ```ruby
 RSpec.configure do |c|
   c.hiera_config = 'spec/fixtures/hiera/hiera.yaml'
 end
 ```
 
-spec/fixtures/hiera/hiera.yaml
-```yaml
----
-:backends:
-  - yaml
-:yaml:
-  :datadir: spec/fixtures/hieradata
-:hierarchy:
-  - common
+Once that is set, you should be able to start using the lookup function
+
+```ruby
+  ntpserver = lookup('ntpserver')
 ```
 
 **Please note:** In-module hiera data depends on having a correct metadata.json file. It is