tiny typo in DDD table

Under "Let’s take the difference between the two matrices or (C = 1) - (C = 0):"

The P=1 row's Diff should be B5+B7

Author: donbowen

docs/code/06_twfe.md

@@ -80,7 +80,7 @@ Let's take the difference between the two matrices or (C = 1) - (C = 0):
 |          | T = 0 | T = 1 | Difference  | 
 | -------- | ----- | ----- | -----   |
 | **P = 0** | $$ \beta_2  $$ | $$ \beta_2 + \beta_5 $$   |  $$ \beta_5 $$ |
-| **P = 1** | $$ \beta_2 + \beta_6 $$ | $$ \beta_2 + \beta_5 + \beta_6 + \beta_7 $$ | $$ \beta_6 + \beta_7 $$  |
+| **P = 1** | $$ \beta_2 + \beta_6 $$ | $$ \beta_2 + \beta_5 + \beta_6 + \beta_7 $$ | $$ \beta_5 + \beta_7 $$  |
 | Difference |  $$ \beta_6 $$   | $$ \beta_6 + \beta_7 $$ | $$ \beta_7 $$   |
 
 where we end up with the main difference of $$ \beta_7 $$. Note that this table logic is also far simpler than having a long list of expectations defined for each combination.