chore(simple-combo): Document changes in behavior when used in forms

Author: IvanKitanov17

CHANGELOG.md

@@ -11,6 +11,10 @@ All notable changes for each version of this project will be documented in this
         - Fractional seconds: S, SS, SSS.
         - Period (Am/Pm): a, aa, aaa, aaaa, aaaaa
 
+### General
+- `IgxSimpleCombo`
+    - **Behavioral Change** When bound to `ngModel` and `formControlName` directives, the model would not be updated when the user types into the input and will only be updated on selection.
+
 ## 17.2.0
 ### New Features
 - `IgxAvatar`