Documentation: some sparsity wording clarifications

Improve the wording for a couple paragraphs in two different manuals
relating to sparse behavior.

Reported-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Elijah Newren <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: newren

Documentation/git-read-tree.txt

@@ -375,10 +375,13 @@ have finished your work-in-progress), attempt the merge again.
 SPARSE CHECKOUT
 ---------------
 
-Note: The `update-index` and `read-tree` primitives for supporting the
-skip-worktree bit predated the introduction of
-linkgit:git-sparse-checkout[1].  Users are encouraged to use
-`sparse-checkout` in preference to these low-level primitives.
+Note: The skip-worktree capabilities in linkgit:git-update-index[1]
+and `read-tree` predated the introduction of
+linkgit:git-sparse-checkout[1].  Users are encouraged to use the
+`sparse-checkout` command in preference to these plumbing commands for
+sparse-checkout/skip-worktree related needs.  However, the information
+below might be useful to users trying to understand the pattern style
+used in non-cone mode of the `sparse-checkout` command.
 
 "Sparse checkout" allows populating the working directory sparsely.
 It uses the skip-worktree bit (see linkgit:git-update-index[1]) to

Documentation/git-sparse-checkout.txt

@@ -15,11 +15,11 @@ SYNOPSIS
 DESCRIPTION
 -----------
 
-This command is used to create sparse checkouts, which means that it
-changes the working tree from having all tracked files present, to only
-have a subset of them.  It can also switch which subset of files are
-present, or undo and go back to having all tracked files present in the
-working copy.
+This command is used to create sparse checkouts, which change the
+working tree from having all tracked files present to only having a
+subset of those files.  It can also switch which subset of files are
+present, or undo and go back to having all tracked files present in
+the working copy.
 
 The subset of files is chosen by providing a list of directories in
 cone mode (the default), or by providing a list of patterns in