[files-pipeline] update docs with note about settings
[files-pipeline] update docs with note about settings

for subclasses.

darkrho/scrapy-scrapy,dangra/scrapy,finfish/scrapy,pawelmhm/scrapy,Parlin-Galanodel/scrapy,finfish/scrapy,ssteo/scrapy,jc0n/scrapy,ssteo/scrapy,pablohoffman/scrapy,finfish/scrapy,rootAvish/scrapy,eLRuLL/scrapy,darkrho/scrapy-scrapy,w495/scrapy,wujuguang/scrapy,eLRuLL/scrapy,pablohoffman/scrapy,taito/scrapy,shaform/scrapy,rootAvish/scrapy,scrapy/scrapy,pablohoffman/scrapy,crasker/scrapy,umrashrf/scrapy,wujuguang/scrapy,crasker/scrapy,arush0311/scrapy,pawelmhm/scrapy,YeelerG/scrapy,elacuesta/scrapy,foromer4/scrapy,taito/scrapy,darkrho/scrapy-scrapy,umrashrf/scrapy,arush0311/scrapy,pawelmhm/scrapy,elacuesta/scrapy,Parlin-Galanodel/scrapy,scrapy/scrapy,starrify/scrapy,starrify/scrapy,GregoryVigoTorres/scrapy,dangra/scrapy,wenyu1001/scrapy,dangra/scrapy,crasker/scrapy,rolando-contrib/scrapy,wenyu1001/scrapy,ArturGaspar/scrapy,foromer4/scrapy,Ryezhang/scrapy,YeelerG/scrapy,ArturGaspar/scrapy,Parlin-Galanodel/scrapy,jc0n/scrapy,w495/scrapy,scrapy/scrapy,redapple/scrapy,eLRuLL/scrapy,kmike/scrapy,barraponto/scrapy,redapple/scrapy,redapple/scrapy,Ryezhang/scrapy,arush0311/scrapy,foromer4/scrapy,rolando-contrib/scrapy,shaform/scrapy,rolando/scrapy,elacuesta/scrapy,wenyu1001/scrapy,kmike/scrapy,jc0n/scrapy,rolando-contrib/scrapy,kmike/scrapy,w495/scrapy,GregoryVigoTorres/scrapy,taito/scrapy,barraponto/scrapy,Ryezhang/scrapy,rolando/scrapy,ssteo/scrapy,ArturGaspar/scrapy,umrashrf/scrapy,rolando/scrapy,rootAvish/scrapy,wujuguang/scrapy,GregoryVigoTorres/scrapy,barraponto/scrapy,shaform/scrapy,YeelerG/scrapy,starrify/scrapy