Add advice for multiple files - https://github.com/koalaman/shellcheck/issues/1920

SC2126.md

@@ -12,6 +12,20 @@ grep foo | wc -l
 grep -c foo
 ```
 
+#### For multiple files
+
+Instead of:
+
+```sh
+grep foo *.log | wc -l
+```
+
+Pipe all the file contents into `grep` (passing the files directly to `grep` causes `-c` to print each file's count separately, rather than the total):
+
+```sh
+cat *.log | grep foo -c
+```
+
 ### Rationale:
 
 This is purely a stylistic issue. `grep` can count lines without piping to `wc`.