Update code owners (#157)

* Update code owners

* Update .github/CODEOWNERS

Co-authored-by: Samir Nasibli <samir.nasibli@intel.com>

* Extend and comment CODEOWNERS

---------

Co-authored-by: Samir Nasibli <samir.nasibli@intel.com>

Author: Alexsandruss

.github/CODEOWNERS

@@ -1,7 +1,15 @@
-# owners and reviewers
-configs             @Alexsandruss
-configs/spmd*       @Alexsandruss @ethanglaser
-sklbench            @Alexsandruss
-*.md                @Alexsandruss @samir-nasibli
-requirements*.txt   @Alexsandruss @ethanglaser
-conda-env-*.yml     @Alexsandruss @ethanglaser
+# benchmarking config files
+configs                    @Alexsandruss
+configs/spmd/*             @ethanglaser
+configs/regular/xgboost*   @razdoburdin
+# sklbench implementation and associated docs
+sklbench                   @Alexsandruss
+# all documentation files
+*.md                       @Alexsandruss
+# dependencies files
+requirements*.txt          @Alexsandruss @ethanglaser
+conda-env-*.yml            @Alexsandruss @ethanglaser
+# repository utilities
+/.*                        @Alexsandruss
+/*.yml                     @Alexsandruss
+/*.toml                    @Alexsandruss