fix: gh-pages deploy folder should be docs

Author: jeffabailey

.github/workflows/mdbook.yml

@@ -1,10 +1,10 @@
 # Workflow for building and deploying a mdBook site to GitHub Pages.
-# - On push to main: deploys to the root of gh-pages.
+# - On push to main: deploys to docs/ on gh-pages.
 # - On pull_request: deploys a preview under pr-preview/pr-<number>/ on gh-pages,
 #   comments the preview URL, and cleans up when the PR closes.
 #
 # Repo Settings required:
-#   Pages -> Source: "Deploy from a branch" -> gh-pages / (root)
+#   Pages -> Source: "Deploy from a branch" -> gh-pages / /docs
 #   Actions -> General -> Workflow permissions: "Read and write permissions"
 #
 # See: https://rust-lang.github.io/mdBook/index.html
@@ -79,6 +79,7 @@ jobs:
         with:
           branch: gh-pages
           folder: ./book
+          target-folder: docs
           clean: true
           clean-exclude: pr-preview