Although I can't see a reason why you can't just add the text to the HTML file, I will still answer your question.
There is no way to add text inside of the HTML tag. The only way that you can add text around HTML is through pseudo elements like the following:
p:before{
content: "today";
color: black;
}
This is not recommended however, due to the fact that the text won't actually exist in the html and will need to be styled to display properly.
A much better solution would be to use javascript
<script>
document.getElementById('todayTag').innerHTML = "today";
</script>
The 'todayTag' refers to an ID that will be placed on the p tag.