Condense index documentation

docs/api/index.md

@@ -5,10 +5,8 @@
 on a Taylor approximation of the log-likelihood. Uses the empirical Fisher
 information matrix as a positive-definite alternative to the Hessian.
 Natural gradient descent equivalence following [Ollivier, 2019](https://arxiv.org/abs/1703.00209).
-- [`ekf.diag_fisher`](ekf/diag_fisher.md) applies an online Bayesian update based 
-on a Taylor approximation of the log-likelihood. Uses the diagonal empirical Fisher
-information matrix as a positive-definite alternative to the Hessian.
-Natural gradient descent equivalence following [Ollivier, 2019](https://arxiv.org/abs/1703.00209).
+- [`ekf.diag_fisher`](ekf/diag_fisher.md) same as `ekf.dense_fisher` but
+uses the diagonal of the empirical Fisher information matrix instead.
 
 ### Laplace approximation
 - [`laplace.dense_fisher`](laplace/dense_fisher.md) calculates the empirical Fisher