I guess this would be like a scrapbook of your relationship - times spent together, places visited etc. Remember, 'a picture speaks a thousand words' - with digital photos it's easier nowadays to show time/date and even location of any meetings. Also, screenshots of video calls etc can be useful. That's my 'take' on what a storybook means...
No, you won’t find storybook mentioned in either the mandatory or support documents requirements, yes send some photos about a dozen various locations various times over the year(s). They want to know you’ve met, and in a meaningful relationship, never overload.
As mentioned by Mattecube, we had to submit about a dozen photos and a screenshot (one day per month) from messenger, showing conversation and video call times. That was it, lucky she kept it all, I am a delete and keep clean guy ! I was also asked for any record of money transactions send to her as proof of relationship, this included things like flowers sent on birthday, Xmas etc
Yes they, the UKBA ask for that in a set of questions in one section of the application. Then you can upload further supporting docs ie snap shot conversations from internet in the additional supporting information I