chore(techdocs): add changeset files

Signed-off-by: Camila Belo <camilaibs@gmail.com>

.changeset/dull-waves-marry.md

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+---
+'@backstage/plugin-techdocs': patch
+---
+
+Create a menu in the sub header of documentation pages, it is responsible for rendering TechDocs addons that allow users to customize their reading experience.

.changeset/nice-parrots-lie.md

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+---
+'@backstage/plugin-techdocs-react': patch
+---
+
+Create a new addon location called "Settings", it is designed for addons that allow users to customize the reading experience in documentation pages.
+
+Usage example:
+
+```tsx
+const TextSize = techdocsModuleAddonsContribPlugin.provide(
+  createTechDocsAddonExtension({
+    name: 'TextSize',
+    location: TechDocsAddonLocations.Settings,
+    component: TextSizeAddon,
+  }),
+);
+```

.changeset/small-eggs-guess.md

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+---
+'@backstage/plugin-techdocs-module-addons-contrib': patch
+---
+
+Create a TechDocs `<TextSize/>` addon that allows users to set a font size in the browser's local storage for the text of documentation pages.
+
+Here's an example on how to use it in a Backstage app:
+
+```diff
+import {
+  DefaultTechDocsHome,
+  TechDocsIndexPage,
+  TechDocsReaderPage,
+} from '@backstage/plugin-techdocs';
+import { TechDocsAddons } from '@backstage/plugin-techdocs-react/alpha';
++import { TextSize } from '@backstage/plugin-techdocs-module-addons-contrib';
+
+const AppRoutes = () => {
+  <FlatRoutes>
+    // other plugin routes
+    <Route path="/docs" element={<TechDocsIndexPage />}>
+      <DefaultTechDocsHome />
+    </Route>
+    <Route
+      path="/docs/:namespace/:kind/:name/*"
+      element={<TechDocsReaderPage />}
+    >
+      <TechDocsAddons>
++       <TextSize />
+      </TechDocsAddons>
+    </Route>
+  </FlatRoutes>;
+};
+```