Add installation notes and restructure environment variables

Updated the NOTES.txt template to include a congratulatory
message upon successful installation of the Paperless-NGX
chart and added a reminder to check the 'main' service for
access details.

In the values.yaml file, the structure of the environment
variables section has been modified for improved clarity
and readability. This rearrangement maintains the existing
configuration while making it easier to understand where
environment variables are defined.

No breaking changes were introduced; the functionality remains
intact.

charts/paperless-ngx/values.yaml

@@ -10,20 +10,19 @@ controllers:
     type: deployment
     replicas: 1
     defaultContainerOptions:
-    image:
-      # -- Image repository
-      repository: ghcr.io/paperless-ngx/paperless-ngx
-      # -- Image pull policy
-      pullPolicy: IfNotPresent
-      # -- Image tag
-      tag: 2.20.0
-
-# -- Environment variables [[ref]](https://docs.paperless-ngx.com/configuration/)
-# @default -- See [values.yaml](./values.yaml)
-env:
-  # -- Set the container timezone
-  TZ: UTC
-  # PAPERLESS_SECRET_KEY: ""
+      image:
+        # -- Image repository
+        repository: ghcr.io/paperless-ngx/paperless-ngx
+        # -- Image pull policy
+        pullPolicy: IfNotPresent
+        # -- Image tag
+        tag: 2.20.0
+        # -- Environment variables [[ref]](https://docs.paperless-ngx.com/configuration/)
+        # @default -- See [values.yaml](./values.yaml)
+        env:
+          # -- Set the container timezone
+          TZ: UTC
+          # PAPERLESS_SECRET_KEY: ""
 
 service:
   # -- Configures service settings for the chart.