After capturing a screenshot on an iPhone, there is immediately an option for you to write texts on it or add some markups on it before it goes to your Camera Roll. You would see a prompt to Save it to Photos or Delete Screenshot after editing it. In cases where you already made the screenshot but weren’t able to tap on Edit, you can still do so later by selecting the particular screenshot and tapping on Edit.
I didn’t know this simple tip before and just thought I would share it for others to save time in editing photos and screenshots. I used to retrieve my photo or screenshot to be edited via iCloud.com’s Camera Roll and open Paint on my Windows laptop to add markups on my photos or screenshots.