t5572: describe '--rebase' tests a little more

It can be hard at first glance to distinguish what is different between
the two tests 'recursive rebasing pull' and 'pull rebase recursing fails
with conflicts' in 't5572-pull-submodule.sh', and to understand how they
relate to the scenarios described in a6d7eb2 (pull: optionally rebase
submodules (remote submodule changes only), 2017-06-23), which
implemented '--recurse-submodules' for 'git pull' and added these tests.

Rename the tests to be more descriptive and add some bullet points
comments describing the different scenarios.

Signed-off-by: Philippe Blain <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: phil-blain

t/t5572-pull-submodule.sh

@@ -101,7 +101,12 @@ test_expect_success " --[no-]recurse-submodule and submodule.recurse" '
 	test_path_is_file super/sub/merge_strategy_4.t
 '
 
-test_expect_success 'recursive rebasing pull' '
+test_expect_success 'pull --rebase --recurse-submodules (remote superproject submodule changes, local submodule changes)' '
+	# This tests the following scenario :
+	# - local submodule has new commits
+	# - local superproject does not have new commits
+	# - upstream superproject has new commits that change the submodule pointer
+
 	# change upstream
 	test_commit -C child rebase_strategy &&
 	git -C parent submodule update --remote &&
@@ -116,7 +121,10 @@ test_expect_success 'recursive rebasing pull' '
 	test_path_is_file super/sub/local_stuff.t
 '
 
-test_expect_success 'pull rebase recursing fails with conflicts' '
+test_expect_success 'pull --rebase --recurse-submodules fails if both sides record submodule changes' '
+	# This tests the following scenario :
+	# - local superproject has new commits that change the submodule pointer
+	# - upstream superproject has new commits that change the submodule pointer
 
 	# local changes in submodule recorded in superproject:
 	test_commit -C super/sub local_stuff_2 &&