add info about using snippets for constants

Author: devalog

fern/products/docs/pages/component-library/custom-components/custom-react-components.mdx

@@ -3,12 +3,14 @@ title: Custom React Components
 subtitle: Add your own React components to enhance your docs
 ---
 
+<Markdown src="/snippets/pro-plan.mdx"/>
+
 You can extend Fern's built-in component library by adding your own custom React components. 
 This allows you to create unique, interactive elements that match your documentation needs.
 
-<Note>Setting up custom react components is part of the pro plan.</Note>
+<Note title="Defining a constant">Don't use a React component to define a constant. Instead, consider using [reusable snippets](/docs/writing-content/reusable-markdown).</Note>
 
-## How does it work
+## How does it work?
 
 <Steps>
   ### Create a React component

fern/products/docs/pages/component-library/custom-components/reusable-markdown.mdx

@@ -5,6 +5,8 @@ description: Reusable, custom markdown snippets to keep content in sync. Edit on
 
 Keep your documentation DRY (Don't Repeat Yourself) by defining a reusable Markdown snippet once, and then referencing it in multiple places. This way, you only need to update the snippet in one place to keep all references in sync.
 
+Reusable snippets work well for constants (API limits, subscription prices, version numbers), repeated warnings or notes, and standardized formatting blocks.
+
 ## Create a reusable snippet
 
 To use reusable snippets, start by creating a new folder in your `fern` project called `snippets`. Inside the `snippets` folder, create a new Markdown file for each snippet you want to define.