*sum: update pages to make them consistent (#14923)

* *sum: update pages to make them consistent

* shasum: remove redundant option

* shasum: update page

pages/common/md5sum.md

@@ -15,7 +15,7 @@
 
 `{{command}} | md5sum`
 
-- Read a file of MD5 sums and filenames and verify all files have matching checksums:
+- Read a file of MD5 checksums and filenames and verify all files have matching checksums:
 
 `md5sum --check {{path/to/file.md5}}`
 
@@ -26,3 +26,7 @@
 - Only show a message when verification fails, ignoring missing files:
 
 `md5sum --ignore-missing --check --quiet {{path/to/file.md5}}`
+
+- Check a known MD5 checksum of a file:
+
+`echo {{known_md5_checksum_of_the_file}} {{path/to/file}} | md5sum --check`