Adds "Supported versions of Django"
Adds "Supported versions of Django"

Adds "Supported versions of Django" section
into "Wagtail's release process" document.

chrxr/wagtail,Toshakins/wagtail,kaedroho/wagtail,zerolab/wagtail,wagtail/wagtail,mixxorz/wagtail,takeflight/wagtail,Toshakins/wagtail,nilnvoid/wagtail,nealtodd/wagtail,takeflight/wagtail,nilnvoid/wagtail,FlipperPA/wagtail,torchbox/wagtail,mixxorz/wagtail,kaedroho/wagtail,nilnvoid/wagtail,mikedingjan/wagtail,mikedingjan/wagtail,Toshakins/wagtail,thenewguy/wagtail,nealtodd/wagtail,gasman/wagtail,thenewguy/wagtail,wagtail/wagtail,jnns/wagtail,FlipperPA/wagtail,jnns/wagtail,gasman/wagtail,kaedroho/wagtail,wagtail/wagtail,mixxorz/wagtail,rsalmaso/wagtail,torchbox/wagtail,zerolab/wagtail,FlipperPA/wagtail,kaedroho/wagtail,gasman/wagtail,iansprice/wagtail,thenewguy/wagtail,gasman/wagtail,kaedroho/wagtail,zerolab/wagtail,wagtail/wagtail,torchbox/wagtail,nutztherookie/wagtail,nealtodd/wagtail,takeflight/wagtail,iansprice/wagtail,timorieber/wagtail,iansprice/wagtail,chrxr/wagtail,nutztherookie/wagtail,iansprice/wagtail,timorieber/wagtail,FlipperPA/wagtail,nutztherookie/wagtail,takeflight/wagtail,nilnvoid/wagtail,nimasmi/wagtail,nimasmi/wagtail,nimasmi/wagtail,thenewguy/wagtail,nealtodd/wagtail,rsalmaso/wagtail,zerolab/wagtail,thenewguy/wagtail,jnns/wagtail,timorieber/wagtail,mixxorz/wagtail,torchbox/wagtail,mixxorz/wagtail,nimasmi/wagtail,gasman/wagtail,wagtail/wagtail,chrxr/wagtail,zerolab/wagtail,mikedingjan/wagtail,jnns/wagtail,mikedingjan/wagtail,rsalmaso/wagtail,timorieber/wagtail,chrxr/wagtail,Toshakins/wagtail,nutztherookie/wagtail,rsalmaso/wagtail,rsalmaso/wagtail