chore(ci): add a pipeline to update documentation

Author: ThibaultBee

.github/workflows/update-documentation.yml

@@ -0,0 +1,17 @@
+name: Update readme.io documentation
+on:
+  push:
+    branches:
+      - master
+jobs:
+  update-documentation:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Update readme.io documentation
+        uses: apivideo/[email protected]
+        with:
+          document-slug: flutter-uploader
+          markdown-file-path: README.md
+          readme-io-api-key: ${{ secrets.README_IO_API_KEY }}
+          make-relative-links-absolute: true