Pick the goal you want to watch and the goal you want to add a datapoint to. Every time you add a datapoint to the first goal, the second goal will get a +1 datapoint added to it, with the details of the first goal's datapoint in the comment.
NOTE THAT THIS WON'T ALWAYS WORK WELL WITH INTEGRATION-BASED GOALS
(e.g. Toggle, Apple Health, etc.) since many of those datapoints are updated, rather than recreated, so only the day's first datapoint will be caught by the recipe.