a11y: newsletter form

[ramiy]

In the about page we have a newsletter form. The <input> fields in the form use placeholder attributes to display the fields.

We need to add <label> fields above each input field, add for attributes to reference to the field, and hide the labels using WordPress screen-reader-text class. This way only screen-readers will "see" the labels.

[DevinWalker]

Sounds good.