📝 docs(custom.mdx): add documentation for custom component

docs/docs/components/custom.mdx

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+import Admonition from "@theme/Admonition";
+
+# Custom Component
+
+---
+
+Used to create a custom component. The code is the class that will be converted to a Custom Component with the fields and formatting you define.
+
+**Params**
+
+- **Code:** The code of the component.
+
+<Admonition type="info" label="Tip">
+
+[Learn more about Custom Components](../guidelines/custom-component)
+
+</Admonition>