Add "Exec platform per toolchain" under review (#280)

Author: comius

README.md

@@ -20,6 +20,7 @@ list.
 
 | Last updated | Title                                                                                                                                                     | Author(s) alias                                                              | Category              |
 | ------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------- | --------------------- |
+|   2022-11-30 | [Exec platform per toolchain](https://docs.google.com/document/d/1-rbP_hmKs9D639YWw5F_JyxPxL2bi6dSmmvj_WXak9M/edit?usp=sharing) | [@comius](https://github.com/comius) [@kotlaja](https://github.com/kotlaja) | Configurability |
 |   2022-10-17 | [Dependency adapters for virtual targets](designs/2022-10-17-dependency-adapter.md) | [@vdye](https://github.com/vdye) | Bazel |
 |   2022-10-11 | [Renaming applicable_licenses](https://docs.google.com/document/d/1uyJjkKbE8kV8EinakaR9q-Un25zCukhoH_dRBkWHSKQ) | [@aiuto](https://github.com/aiuto) | Configuration |
 |   2022-07-07 | [Enabling Global exec_groups](https://github.com/bazelbuild/proposals/new/main/designs/2022-07-07_global_exec_groups.md)                           | [@susinmotion](https://github.com/susinmotion)  |  Configurability     |