Created SC1145 (markdown)

SC1145.md

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+## Unknown external-sources value. Expected true/false.
+
+### Problematic code:
+
+`.shellcheckrc`:
+
+```sh
+external-sources=maybe
+```
+
+### Correct code:
+
+```sh
+external-sources=true
+```
+
+### Rationale:
+
+The `external-sources` [[directive]] expects a value of `true` or `false`.
+
+### Exceptions:
+
+None.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!