How do I add some text onto the divider between rows?

Example (with "OR" as text):

The idea is that on collapse of columns—i.e.: view on mobile sized-screen—it will appear betwixt submit and Click me.

How do I add some text onto the divider between rows?

Why don't you use a .span between your two forms ?

<div class="container">
    <div class="row">
        <div class="span5">
            form 1
        </div>
        <div class="span2">OR</div>
        <div class="span5">
            form 2
        </div>
    </div>
</div>

Demo (jsfiddle)