enabling diagram examples

Author: cblanquera

README.md

@@ -47,7 +47,7 @@ model Post {
 
 With a plugin, it can produce a schema diagram like this:
 
-```text
+```mermaid
 classDiagram
   class User {
     String id

docs/getting-started.md

@@ -95,7 +95,7 @@ working directory.
 
 You should now have `generated/schema.mmd`:
 
-```text
+```mermaid
 classDiagram
   class User {
     String id