Add details of shellcheck disable=all as it seems to be missing

Ignore.md

@@ -73,3 +73,15 @@ Add a [[directive]] at the top of the file:
 ```
 
 Note that the [[directive]] must be on the first line after the shebang with versions before 0.4.6. As of 0.4.6 comments and whitespace are allowed before file-wide directives.
+
+
+### Ignoring all errors in a file (0.8+)
+Add a [[directive]] at the top of the file:
+
+```sh
+#!/bin/sh
+# shellcheck disable=all
+```
+
+Note that the [[directive]] must be on the first non-commented/non-whitespace line after the shebang with versions after 0.4.6.
+