Removed mentions of group from the readme

README.md

@@ -97,7 +97,6 @@ import ecs;
     - [Traversal and layout](#Traversal-and-layout)
 - [System options](#system-options)
   - [`opts::interval<ms, us>`](#optsintervalms-us)[<img src="https://godbolt.org/favicon.ico" width="16">](https://godbolt.org/z/aGM86KWdf)
-  - [`opts::group<group number>`](#optsgroupgroup-number)[<img src="https://godbolt.org/favicon.ico" width="16">](https://godbolt.org/z/ezoq17fbr)
   - [`opts::manual_update`](#optsmanual_update)[<img src="https://godbolt.org/favicon.ico" width="16">](https://godbolt.org/z/TxvndcTEq)
   - [`opts::not_parallel`](#optsnot_parallel)[<img src="https://godbolt.org/favicon.ico" width="16">](https://godbolt.org/z/MK9xcTedq)
 - [Variant components](#variant-components)
@@ -344,32 +343,6 @@ rt.make_system<ecs::opts::interval<16, 667>>([](int const&) {
 ```
 
 
-### `opts::group<N>`[<img src="https://godbolt.org/favicon.ico" width="32">](https://godbolt.org/z/ezoq17fbr)
-Systems can be segmented into groups by passing along `opts::group<N>`, where `N` is a compile-time integer constant, as a template parameter to `ecs::make_system`. Systems are roughly executed in the order they are made, but groups ensure absolute separation of systems. Systems with no group id specified are put into the default group 0.
-
-```cpp
-rt.make_system<ecs::opts::group<1>>([](int const&) {
-    std::cout << "hello from group one\n";
-});
-rt.make_system<ecs::opts::group<-1>>([](int const&) {
-    std::cout << "hello from group negative one\n";
-});
-rt.make_system([](int const&) { // same as 'ecs::opts::group<0>'
-    std::cout << "hello from group whatever\n";
-});
-// ...
-rt.add_component(0, int{});
-rt.update();
-```
-
-Running the above code will print out
-> hello from group negative one\
-> hello from group whatever\
-> hello from group one
-
-**Note:** systems from different groups are never executed concurrently, and all systems in one group will run to completion before the next group is run.
-
-
 ### `opts::manual_update`[<img src="https://godbolt.org/favicon.ico" width="32">](https://godbolt.org/z/TxvndcTEq)
 Systems marked as being manually updated will not be added to the scheduler, and will thus require the user to call the `system::run()` function themselves.
 Calls to `ecs::runtime::commit_changes()` will still cause the system to respond to changes in components.