Add documentation for how to use alternative image tags
Add documentation for how to use alternative image tags

This adds documentation for alternative image tags such as `<picture>`
and `<amp-img>`.

wagtail/wagtail,gasman/wagtail,takeflight/wagtail,wagtail/wagtail,zerolab/wagtail,zerolab/wagtail,takeflight/wagtail,timorieber/wagtail,kaedroho/wagtail,thenewguy/wagtail,torchbox/wagtail,thenewguy/wagtail,kaedroho/wagtail,kaedroho/wagtail,timorieber/wagtail,mixxorz/wagtail,takeflight/wagtail,rsalmaso/wagtail,thenewguy/wagtail,thenewguy/wagtail,nimasmi/wagtail,gasman/wagtail,gasman/wagtail,FlipperPA/wagtail,mixxorz/wagtail,kaedroho/wagtail,jnns/wagtail,rsalmaso/wagtail,zerolab/wagtail,kaedroho/wagtail,FlipperPA/wagtail,torchbox/wagtail,nimasmi/wagtail,nimasmi/wagtail,zerolab/wagtail,wagtail/wagtail,nimasmi/wagtail,FlipperPA/wagtail,timorieber/wagtail,rsalmaso/wagtail,mixxorz/wagtail,jnns/wagtail,mixxorz/wagtail,zerolab/wagtail,jnns/wagtail,gasman/wagtail,rsalmaso/wagtail,torchbox/wagtail,mixxorz/wagtail,wagtail/wagtail,torchbox/wagtail,jnns/wagtail,timorieber/wagtail,wagtail/wagtail,FlipperPA/wagtail,gasman/wagtail,takeflight/wagtail,thenewguy/wagtail,rsalmaso/wagtail