chore(*): updating grid readme with the new props

Author: ChronosSF

projects/igniteui-angular/src/lib/grids/README.md

@@ -185,6 +185,7 @@ Below is the list of all inputs that the developers may set to configure the gri
 |`evenRowCSS`|string|Additional styling classes applied to all even rows in the grid.|
 |`oddRowCSS`|string|Additional styling classes applied to all odd rows in the grid.|
 |`paginationTemplate`|TemplateRef|You can provide a custom `ng-template` for the pagination part of the grid.|
+|`groupStrategy`| IGridGroupingStrategy | Provides custom group strategy to be used when grouping |
 |`groupingExpressions`| Array | The group by state of the grid.
 |`groupingExpansionState`| Array | The list of expansion states of the group rows. Contains the expansion state(expanded: boolean) and an unique identifier for the group row (Array<IGroupByExpandState>) that contains a list of the group row's parents described via their fieldName and value.
 |`groupsExpanded`| boolean | Determines whether created groups are rendered expanded or collapsed.  |