Add note about password requirements per charts PR#21072 (#21271)

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Signed-off-by: bitpushr <91350598+bitpushr@users.noreply.github.com>

charts/premium/nextcloud/docs/installation-notes.md

@@ -29,10 +29,16 @@ The following configurations must be set during initial setup in order for Nextc
 
 1. An initial admin username needs to be set
 
-2. An initial admin password needs to be set
+2. An initial admin password needs to be set. 
 
 3. Default phone region needs to be set (if you are unsure about your region, you can find your code for your region in this [wiki](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2#Officially_assigned_code_elements))
 
+:::caution[Password Requirements]
+
+Due to limitations when converting YAML to JSON, the passwords used with Nextcloud for admin and Postgres must **only** start with a letter or number. If you attempt to use a password that starts with a symbol, e.g. '%', Nextcloud will fail to install as it will be unable to convert the YAML to JSON.
+
+:::
+
 ### Optional Addons
 
 1. Notify Push (Allows Nextcloud to notify clients of changes, instead of clients having to poll. A Notify Push container will be deployed automatically). This is highly recommended to keep enabled.