Update docs for Conduit and Dendrite: replace "Notes" with "Warnings" plus the warning symbol

The information is important and should deserve clear attention.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/configuring-playbook-conduit.md

@@ -2,7 +2,7 @@
 
 By default, this playbook configures the [Synapse](https://github.com/element-hq/synapse) Matrix server, but you can also use [Conduit](https://conduit.rs).
 
-**Notes**:
+⚠️ **Warnings**:
 
 - **You can't switch an existing Matrix server's implementation** (e.g. Synapse -> Conduit). Proceed below only if you're OK with losing data or you're dealing with a server on a new domain name, which hasn't participated in the Matrix federation yet.
 

docs/configuring-playbook-dendrite.md

@@ -2,7 +2,7 @@
 
 By default, this playbook configures the [Synapse](https://github.com/element-hq/synapse) Matrix server, but you can also use [Dendrite](https://github.com/matrix-org/dendrite).
 
-**Notes**:
+⚠️ **Warnings**:
 
 - **You can't switch an existing Matrix server's implementation** (e.g. Synapse -> Dendrite). Proceed below only if you're OK with losing data or you're dealing with a server on a new domain name, which hasn't participated in the Matrix federation yet.