Nimble Rich Text Editor and Viewer Spec Document (#1289)

# Pull Request

## 🤨 Rationale

Creating spec for `nimble-rich-text-editor` and
`nimble-rich-text-viewer` components.
Issue: #1288 

## 👩‍💻 Implementation

This PR contains the nimble spec document for the new nimble component
addition. The spec document consists of a design discussion for the
`nimble-rich-text-editor` and `nimble-rich-text-viewer` components and
explains the external libraries used for the development of a rich text
editor.

## 🧪 Testing

N/A

## ✅ Checklist

N/A

change/@ni-nimble-components-02d33e01-7578-482d-aa7f-8f592617a882.json

@@ -0,0 +1,7 @@
+{
+  "type": "none",
+  "comment": "Add spec document for nimble rich text editor and nimble rich text viewer",
+  "packageName": "@ni/nimble-components",
+  "email": "[email protected]",
+  "dependentChangeType": "none"
+}

packages/nimble-components/src/rich-text-viewer/specs/README.md

@@ -0,0 +1,3 @@
+# Nimble Rich Text Viewer
+
+The spec of this component is added as part of the [`/rich-text-editor/specs/README.md`](../../rich-text-editor/specs/README.md)