doc: add mroonga_default_tokenizer
doc: add mroonga_default_tokenizer

naoa/mroonga,yoku0825/mroonga,yoku0825/mroonga,mroonga/mroonga,naoa/mroonga,mroonga/mroonga,yoku0825/mroonga,mroonga/mroonga,mroonga/mroonga,yoku0825/mroonga,yoku0825/mroonga,naoa/mroonga,yoku0825/mroonga,naoa/mroonga,naoa/mroonga,naoa/mroonga