improve the documentation

docs/src/docPages/api/schema/get-schema.md

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+# Get the underlying ProseMirror schema
+
+There are a few use cases where you need to work with the underlying schema. You’ll need that if you’re using the tiptap collaborative text editing features or if you want to manually render your content as HTML.
+
+## With an Editor
+If you need this on the client side and need an editor instance anyway, it’s available through the editor:
+
+```js
+import { Editor } from '@tiptap/core'
+import Document from '@tiptap/extension-document'
+import Paragraph from '@tiptap/extension-paragraph'
+import Text from '@tiptap/extension-text'
+
+const editor = new Editor({
+  extensions: [
+    new Document,
+    new Paragraph,
+    new Text,
+    // add more extensions here
+  ])
+})
+
+const schema = editor.schema
+```
+
+## Without an Editor
+If you just want to have the schema *without* initializing an actual editor, you can use the `getSchema` helper function. It needs an array of available extensions and conveniently generates a ProseMirror schema for you:
+
+```js
+import { getSchema } from '@tiptap/core'
+import Document from '@tiptap/extension-document'
+import Paragraph from '@tiptap/extension-paragraph'
+import Text from '@tiptap/extension-text'
+
+const schema = getSchema([
+  new Document,
+  new Paragraph,
+  new Text,
+  // add more extensions here
+])
+```