add bootstrapify as a submodule

.gitmodules

@@ -46,3 +46,6 @@
 [submodule "sort_tags"]
 	path = sort_tags
 	url = https://github.com/ingwinlu/sort_tags.git
+[submodule "bootstrapify"]
+	path = bootstrapify
+	url = https://github.com/ingwinlu/pelican-bootstrapify.git