Track the best path for a submodule that was added

For Agda, this is a proxy for 'root directory' of a project

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

layouts/shortcodes/codeblock.html

@@ -1,6 +1,7 @@
 {{ partial "geturl.html" (dict "scratch" .Scratch "path" (.Get 1) "siteSourceUrl" .Site.Params.siteSourceUrl "submoduleLinks" .Site.Data.submodules) }}
 {{ $groupconfig := dict
        "url" (.Scratch.Get "bestUrl")
+       "basePath" (.Scratch.Get "bestPath")
        "path" (.Get 1)
        "comment" ", entire file"
        "code" (readFile (printf "code/%s" (.Get 1)))