Create dependabot.yml

Only pip packages and ignore pygments, related to https://github.com/searx/searx/pull/2206

.github/dependabot.yml

@@ -0,0 +1,12 @@
+# https://help.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+version: 2
+updates:
+  - package-ecosystem: "pip"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "friday"
+    open-pull-requests-limit: 5
+    target-branch: "update-dependencies"
+    ignore:
+      - dependency-name: "pygments"