Make it clear the PostgreSQL password should be supplied

If the PostgreSQL password is not explicitly supplied during chart
installation or upgrades, a random password is generated and used when
initialising the database. On future upgrades a new password is
generated in the PostgreSQL Secret resource but the database password is
not changed, so the two go out of sync. This leads to NetBox and its
rqworker failing to start.

Closes #36

README.md

@@ -7,7 +7,10 @@ data center infrastructure management (DCIM) tool.
 
 ```shell
 $ helm repo add bootc https://charts.boo.tc
-$ helm install netbox bootc/netbox
+$ helm install netbox \
+  --set postgresql.postgresqlPostgresPassword=[password1] \
+  --set postgresql.postgresqlPassword=[password2] \
+  bootc/netbox
 ```
 
 ## Prerequisites
@@ -22,7 +25,10 @@ To install the chart with the release name `my-release` and default configuratio
 
 ```shell
 $ helm repo add bootc https://charts.boo.tc
-$ helm install my-release bootc/netbox
+$ helm install my-release \
+  --set postgresql.postgresqlPostgresPassword=[password1] \
+  --set postgresql.postgresqlPassword=[password2] \
+  bootc/netbox
 ```
 
 The default configuration includes the required PostgreSQL and Redis database
@@ -38,6 +44,15 @@ $ helm delete my-release
 
 ## Upgrading
 
+### Bundled PostgreSQL
+
+When upgrading or changing settings and using the bundled Bitnami PostgreSQL
+sub-chart, you **must** provide the `postgresql.postgresqlPassword` at minimum.
+Ideally you should also upply the `postgresql.postgresqlPostgresPassword` and,
+if using replication, the `postgresql.replication.password`. Please see the
+[upstream documentation](https://github.com/bitnami/charts/tree/master/bitnami/postgresql#upgrading)
+for further information.
+
 ### From 2.x to 3.x
 
 * NetBox 2.10.4 or above is required