Add publish date on CI (purescript-contrib#456)

* Add publish date to book (on website)

* Separate section and print PS version

* PureScript available in mdbook build

Author: andys8

.github/workflows/mdbook.yml

@@ -16,6 +16,17 @@ jobs:
         with:
           mdbook-version: 'latest'
 
+      - name: Set up PureScript toolchain
+        uses: purescript-contrib/setup-purescript@main
+
+      - name: Add version section
+        run: |
+          version=$(purs --version)
+          today=$(date -I)
+          echo -e "\n## Release\n" >> README.md
+          echo -e "PureScript v$version\n" >> README.md
+          echo -e "Published on $today" >> README.md
+
       - run: mdbook build
 
       - name: Deploy