Add example of fetching themes.

README.md

@@ -23,3 +23,30 @@ action "Filters for GitHub Actions" {
   args = "branch master"
 }
 ```
+
+Want to dynamically fetch themes before building? Use [this action](https://github.com/marketplace/actions/git-actions) like this
+
+```
+workflow "Hugo build" {
+  resolves = [
+    "Hugo Action",
+  ]
+  on = "push"
+}
+
+action "Fetch git submodules" {
+  uses = "srt32/git-actions@master"
+  args = "cd themes && git clone https://github.com/zyro/hyde-x"
+}
+
+action "Hugo Action" {
+  uses = "srt32/hugo-action@master"
+  needs = ["Filters for GitHub Actions", "Fetch git submodules"]
+  args = "--theme=hyde-x"
+}
+
+action "Filters for GitHub Actions" {
+  uses = "actions/bin/filter@b2bea0749eed6beb495a8fa194c071847af60ea1"
+  args = "branch master"
+}
+```