Comment by Vivtek

It's pretty common on Twitter if you've got more to say than fits in a single tweet. There are even tools to let you manage it (i.e. write a thing and break it up and post individual tweets in order).

Sometimes you'll see them numbered like /1, or if the author knows how many there will be in advance, 1/13, 2/13, etc.

It's not uncommon to put a separate link in many of the individual tweets in the series.