update NewsMD

Author: vyudu

NEWS.md

@@ -1,3 +1,22 @@
+# ModelingToolkit v10 Release Notes
+
+### Callbacks
+
+Callback semantics have changed.
+  - There is a new `Pre` operator that is used to specify which values are before the callback. 
+    For example, the affect `A ~ A + 1` should now be written as `A ~ Pre(A) + 1`. This is 
+    **required** to be specified - `A ~ A + 1` will now be interpreted as an equation to be
+    satisfied after the callback (and will thus error since it is unsatisfiable).
+
+  - All parameters that are changed by a callback must be declared as discrete parameters to
+    the callback constructor, using the `discrete_parameters` keyword argument.
+
+```julia
+event = SymbolicDiscreteCallback(
+    [t == 1] => [p ~ Pre(p) + 1], discrete_parameters = [p])
+```
+
+
 # ModelingToolkit v9 Release Notes
 
 ### Upgrade guide

docs/src/basics/Events.md

@@ -25,7 +25,7 @@ the event occurs). These can both be specified symbolically, but a more [general
 functional affect](@ref func_affects) representation is also allowed, as described
 below.
 
-## Symbolic Callback Semantics (changed in V10)
+## Symbolic Callback Semantics
 
 In callbacks, there is a distinction between values of the unknowns and parameters
 *before* the callback, and the desired values *after* the callback. In MTK, this