fix: docs: 140-shared-extensions.mdx: fix example

The description of the example did not match the example

Author: jlecordier

content/200-orm/200-prisma-client/300-client-extensions/140-shared-extensions.mdx

@@ -30,8 +30,9 @@ To import the `find-or-create` extension from the example above, and wrap your c
 ```ts
 import findOrCreate from 'prisma-extension-find-or-create'
 
-const prisma = new PrismaClient().$extends(findOrCreate)
-const user = await prisma.user.findOrCreate()
+const prisma = new PrismaClient()
+const xprisma = prisma.$extends(findOrCreate)
+const user = await xprisma.user.findOrCreate()
 ```
 
 When you call a method in an extension, use the constant name from your `$extends` statement, not `prisma`. In the above example,`xprisma.user.findOrCreate` works, but `prisma.user.findOrCreate` does not, because the original `prisma` is not modified.