docs(README): Adds Supported Lookups section guide.

* Explains supported lookup types (`:priority` and `:hash`)
* Includes examples

Co-authored-by: Sarah Young <sarahseewhy@gmail.com>
Co-authored-by: Alex Wilson <a.wilson@alumni.warwick.ac.uk>

README.md

@@ -20,6 +20,7 @@ mYs3cR3TpAs5W0rD
 ## Contents
 
 - [Install](#install)
+- [Supported Lookups](#supported-lookups)
 - [Configuration](#configuration)
   - [Region](#region)
   - [Credentials](#credentials)
@@ -45,6 +46,31 @@ Install the dependencies before attempting to use the gem:
 bundle install
 ```
 
+## Supported Lookups
+
+hiera-secrets-manager supports `:priority` (single value) and `:hash` (key-value pair) lookups, but not `:array`.
+
+### Priority Lookup
+
+```puppet
+# In environment 'production' with 'production/system/my-secret' set as 'some-password'
+$secret = hiera('system/my-secret')
+
+notice($secret) # prints 'Notice: Scope(Class[main]): some-password'
+```
+
+### Hash Lookup
+
+```puppet
+# In environment 'production' with 'production/system/my-secret' set as pairs 'foo:bar' and 'baz:zap'
+$secret = hiera_hash('system/my-secret')
+
+notice($secret['foo']) # prints 'Notice: Scope(Class[main]): bar'
+notice($secret['baz']) # prints 'Notice: Scope(Class[main]): zap'
+
+notice($secret) # prints 'Notice: Scope(Class[main]): {"foo"=>"bar", "baz"=>"zap"}'
+```
+
 ## Configuration
 
 Hiera Secrets Manager is configurable and the configuration has three required fields to operate: region, access_key_id, and secret_access_key.