b2sum, md5sum, sha*sum: add --ignore-missing example (#7929)

pages/common/md5sum.md

@@ -11,10 +11,18 @@
 
 `md5sum {{path/to/file1}} {{path/to/filen2}}`
 
-- Read a file of MD5SUMs and verify all files have matching checksums:
-
-`md5sum -c {{path/to/file.md5}}`
-
 - Calculate a MD5 checksum from the standard input:
 
 `echo "{{text}}" | md5sum`
+
+- Read a file of MD5SUMs and verify all files have matching checksums:
+
+`md5sum --check {{path/to/file.md5}}`
+
+- Only show a message for missing files or when verification fails:
+
+`md5sum --check --quiet {{path/to/file.md5}}`
+
+- Only show a message for files for which verification fails, ignoring missing files:
+
+`md5sum --ignore-missing --check --quiet {{path/to/file.md5}}`