Open up your image and select your desired color for your text watermark, now select the text tool and type your text, fill your page with the text like this.
Once you’ve filled your page press “ctrl + t” to transform it, just rotate it slightly, like this.
Now lower the opacity by quite abit as we dont want to spoil the picture. ive lowered mine down to 20% but i think between 10-20% is fine.
thats it all done, now save your image.