Add the data-fusion figure to the card

README.md

@@ -34,6 +34,10 @@ This is the ACS-housing task of [Cross-Block Conditioning in Deep Boltzmann Mach
 
 ## What fusion data look like
 
+![Two sources that share covariates and never overlap on the outcomes](datafusion.png)
+
+Each group of respondents answers one of the two surveys, and the block the other survey collected is unobserved for them; only the covariates are shared. In this dataset the two sources are a labor-and-income block ($Y_A$, the `ya_` columns) and a housing block ($Y_B$, the `yb_` columns), and the common variables are demographics ($X$, the `x_` columns).
+
 | rows | $X$ (demographics) | $Y_A$ (labor and income) | $Y_B$ (housing) |
 |---|:---:|:---:|:---:|
 | panel A (train, `source == "A"`) | observed | observed | *missing* |