Add webassets project

Webassets enables SCSS compilation and asset minification
The pelican-assets plugin was added to integrate it into Pelican
diff --git a/.gitmodules b/.gitmodules
index 2c5f24e..da4e0da 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,6 @@
 [submodule "static/js/lw-timeago"]
 	path = static/js/lw-timeago
 	url = https://github.com/pR0Ps/lw-timeago.git
+[submodule "plugins/assets"]
+	path = plugins/assets
+	url = https://github.com/pR0Ps/pelican-assets.git