docs(setup_env): show HIGHEST_TORCH_GROUP/LOWEST_TORCH_GROUP usage

Export both from the Makefile so they're available to any Make-
invoked subprocess, and reference them via bash fallback expansion
in setup_env.sh's help examples instead of hardcoding the literal
group names — keeps the documented example in sync with the same
alias the Makefile targets already use.

Author: guru-desh

Makefile

@@ -58,6 +58,8 @@ VENV_TUTORIAL ?= .venv-tutorial
 # when the project's torch version bounds change.
 HIGHEST_TORCH_GROUP := torch_2_11
 LOWEST_TORCH_GROUP := torch_2_8
+export HIGHEST_TORCH_GROUP
+export LOWEST_TORCH_GROUP
 
 # Torch dependency group (pyproject.toml [dependency-groups]) that every
 # environment-building target (env, test, test-smoke, docs, ...) pins to.

scripts/make/setup_env.sh

@@ -136,8 +136,8 @@ show_help() {
     echo "  $0 --python-version 3.11                               # Setup with dev group only"
     echo "  $0 --python-version 3.11 --with-docs                   # Setup with dev and docs groups"
     echo "  $0 --python-version 3.11 --all-groups                                    # Setup with all non-conflicting groups"
-    echo "  TORCH_GROUP=torch_2_11 $0 --python-version 3.11 --all-groups             # Setup with all groups and torch 2.11"
-    echo "  TORCH_GROUP=torch_2_8 $0 --python-version 3.11 --all-groups              # Setup with all groups and torch 2.8"
+    echo "  TORCH_GROUP=\${HIGHEST_TORCH_GROUP:-torch_2_11} $0 --python-version 3.11 --all-groups  # Setup with all groups and the highest torch version"
+    echo "  TORCH_GROUP=\${LOWEST_TORCH_GROUP:-torch_2_8} $0 --python-version 3.11 --all-groups   # Setup with all groups and the lowest torch version"
     echo "  $0 --python-version 3.11 --venv .venv-exp              # Setup with custom venv name"
     echo "  $0 --python-version 3.11 --with-docs --venv .venv-exp  # Setup with docs group and custom venv name"
     echo "  $0 --python-version 3.12                               # Setup with Python 3.12"