Missing SECURITY.md about mojo

[sergiotarxz]

#2151 fixes this issue, but maybe there is something else which should be added.

[kraih]

Are there any actual advantages to having the file? Please don't open a PR, a core team member will write the content if we decide it's worth having.

[sergiotarxz]

Github says:

To give people instructions for reporting security vulnerabilities in your project, you can add a SECURITY.md file to your repository's root, docs, or .github folder. When someone creates an issue in your repository, they will see a link to your project's security policy.

If someone finds a security issue in the code is possible that they have problems reporting it, searching for the correct email address to contact for example, SECURITY.md helps them having a clear point in the code where they can find all the instructions to report an issue.

[kraih]

Since we already have CONTRIBUTING.md, this seems a bit redundant.

[sergiotarxz]

Probably true, feel free to close.