chore(Tactic/FunProp): document that config options must come before … (#35987)

…the discharger

This being undocumented just bit me: let's make the documentation clearer

Author: grunweg

Mathlib/Tactic/FunProp/Elab.lean

@@ -36,6 +36,7 @@ documentation for `Mathlib/Tactic/FunProp.lean` for a detailed explanation.
 * `fun_prop [c, ...]` will unfold the constant(s) `c`, ... before decomposing `f`.
 * `fun_prop (config := cfg)` sets advanced configuration options using `cfg : FunProp.Config`
   (see `FunProp.Config` for details).
+  These options can be combined: `fun_prop (config := cfg) (disch := tac) [c]`
 
 Examples: