Extract site preview README instructions into bb site-preview

Author: teodorlu

README.md

@@ -138,6 +138,8 @@ clojure -M:clay -A:markdown
 quarto preview site
 ```
 
+(`bb site-preview` will run these two commands for you.)
+
 This will open a browser displaying the site locally.
 
 If you would like to preview a single file, then add the path relative to `src`:

bb.edn

@@ -0,0 +1,4 @@
+{:tasks
+ {site-preview {:doc "Build site with Quarto and preview"
+                :task (do (clojure "-M:clay -A:markdown")
+                          (shell "quarto preview site"))}}}