ci: create Dependabot config file (#730)

* Create Dependabot config file

* ci: pointing markdown package updates to rafe

* ci: fixing a typo

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>
Co-authored-by: Jon Ursenbach <jon@ursenba.ch>

.github/dependabot.yml

@@ -0,0 +1,29 @@
+version: 2
+updates:
+- package-ecosystem: npm
+  directory: "/"
+  schedule:
+    interval: weekly
+  open-pull-requests-limit: 10
+  reviewers:
+  - erunion
+  labels:
+  - dependencies
+- package-ecosystem: npm
+  directory: "/packages/markdown"
+  schedule:
+    interval: weekly
+  open-pull-requests-limit: 10
+  reviewers:
+  - rafegoldberg
+  labels:
+  - dependencies
+- package-ecosystem: npm
+  directory: "/packages/markdown-magic"
+  schedule:
+    interval: weekly
+  open-pull-requests-limit: 10
+  reviewers:
+  - rafegoldberg
+  labels:
+  - dependencies