fcntl.2: Further tweaks to F_SEAL_FUTURE_WRITE text

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/fcntl.2

@@ -1527,8 +1527,10 @@ pending on the file,
 all outstanding writes will be discarded.
 .TP
 .BR F_SEAL_FUTURE_WRITE " (since Linux 5.1)"
-If this seal is set, the contents of the file can be modified only from
-existing writable mappings that were created prior to the seal being set.
+The effect of this seal is similar to
+.BR F_SEAL_WRITE ,
+but the contents of the file can still be modified via
+shared writable mappings that were created prior to the seal being set.
 Any attempt to create a new writable mapping on the file via
 .BR mmap (2)
 will fail with
@@ -1537,10 +1539,10 @@ Likewise, an attempt to write to the file via
 .BR write (2)
 will fail with
 .BR EPERM .
-This is useful in situations where existing writable mapped
-regions need to be kept intact while preventing any future writes.
-For example, to share a
-read-only memory buffer to other processes that only the sender can write to.
+.IP
+Using this seal,
+one process can create a memory buffer that it can continue to modify
+while sharing that buffer on a "read-only" basis with other processes.
 .\"
 .SS File read/write hints
 Write lifetime hints can be used to inform the kernel about the relative