Language and severity not always in the examples

[atombrella]

As the header says, there are some sample rules that do not contain the language and severity properties.

One example is https://github.com/returntocorp/semgrep-docs/blob/main/docs/writing-rules/rule-syntax.md#complete-useless-comparison

Thank you for a great tool! :) I've used it to find Python code that can be cleaned up, and made more consistent (mostly in unittest classes).