POSTS / Remove `A11y: Screenreaders already announce <img> elements as an image.` Warnings

Referring to this issue A11y is never happy when creating a element, if your img element doesn’t have a proper alt field, just give it a not-so-unproper description will help.

For example in markdown:

![one barking dog](xxx.com/one/pic) is much better than ![image](xxx.com/one/pic)

I met this warning while deploying this blog via Hakuba.