docs: fix directory name
docs: fix directory name

Saying that "If you have ``Blog`` directory", the directory name
must be Blog, not blog.

bcit-ci/CodeIgniter4,samsonasik/CodeIgniter4,samsonasik/CodeIgniter4,samsonasik/CodeIgniter4,lonnieezell/CodeIgniter4,kenjis/CodeIgniter4,lonnieezell/CodeIgniter4,bcit-ci/CodeIgniter4,kenjis/CodeIgniter4,samsonasik/CodeIgniter4,lonnieezell/CodeIgniter4,bcit-ci/CodeIgniter4,kenjis/CodeIgniter4,bcit-ci/CodeIgniter4,lonnieezell/CodeIgniter4,bcit-ci/CodeIgniter4,samsonasik/CodeIgniter4,kenjis/CodeIgniter4,lonnieezell/CodeIgniter4,lonnieezell/CodeIgniter4,kenjis/CodeIgniter4,samsonasik/CodeIgniter4