Create .add-doc-link.yaml (#719)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: julia-pfarr

.github/workflows/.add-doc-link.yaml

@@ -0,0 +1,17 @@
+---
+name: Read the Docs PR preview
+on:
+    pull_request_target:
+        types:
+        -   opened
+
+permissions:
+    pull-requests: write
+
+jobs:
+    pr-preview-link:
+        runs-on: ubuntu-latest
+        steps:
+        -   uses: readthedocs/actions/preview@v1
+            with:
+                project-slug: bids-website