add mention of FTP server storage in media storage intro
add mention of FTP server storage in media storage intro

At the beginning of this doc, in "Specifying where to store the media" feature details, FTP server storage mention was missing
elacuesta/scrapy,elacuesta/scrapy,starrify/scrapy,starrify/scrapy,pawelmhm/scrapy,pawelmhm/scrapy,pablohoffman/scrapy,pablohoffman/scrapy,dangra/scrapy,pawelmhm/scrapy,scrapy/scrapy,starrify/scrapy,elacuesta/scrapy,scrapy/scrapy,scrapy/scrapy,dangra/scrapy,dangra/scrapy,pablohoffman/scrapy