add manual dockerhub trigger

.github/workflows/README.md

@@ -0,0 +1,12 @@
+# Instructions on how to trigger Dockerhub.yml github workflow manually for a specific branch:
+
+Run the following in your command line with your github token (you can replace the branch name in "ref"):
+```
+curl -X POST \
+  -H "Authorization: Bearer YOUR_PERSONAL_ACCESS_TOKEN" \
+  -H "Accept: application/vnd.github+json" \
+  https://api.github.com/repos/usdot-fhwa-stol/carma-platform/actions/workflows/dockerhub.yml/dispatches \
+  -d '{
+    "ref": "develop-humble"
+  }'
+```

.github/workflows/dockerhub.yml

@@ -9,6 +9,8 @@ on:
       - "release/*"
     tags:
       - "carma-system-*"
+     workflow_dispatch:
+
 jobs:
   dockerhub:
     uses: usdot-fhwa-stol/actions/.github/workflows/dockerhub.yml@main