Short explanation of severity scale

[0xsomnus]

I think we should add a short description of what each severity entails to make things clearer to the client. For example, ConsenSys uses this:

Minor issues are subjective in nature. They are typically suggestions around best practices or readability. Code maintainers should use their own judgment as to whether to address such issues.
Medium issues are objective in nature but are not security vulnerabilities. These should be addressed unless there is a clear reason not to.
Major issues are security vulnerabilities that may not be directly exploitable or may require certain conditions in order to be exploited. All major issues should be addressed.
Critical issues are directly exploitable security vulnerabilities that need to be fixed.