Updated readme, contributing, security and issue templates

[timsun28]

Base on the following issue.

Copied the CONTRIBUTING file from the root of the project, so it will show up in the GitHub left hand side menu. Copied templates for issues from collection2 repository, seeing they are quite generic and useful as a start.

Added security.md based on collection2 policy, so it can be updated here once version 4.0 releases with meteor 3 support. I couldn't find anything about the minimum version that this package needs and we could add something here for meteor-roles 4 (and/or 2 and 1).

Added common badges to the readme, only removed the lgtm badge seeing it is no longer supported. It is possible to add a GitHub CodeQL badge, but I'm not sure if it would be possible to add it to this repository.

Also put the readme text through a grammar check and some small improvements.

[Edit]: In the original issue, the following was also mentioned: "Repository admins accept content reports" I couldn't really find what this meant online, but if someone could point me in the right direction, I am happy to update this pull request.

[jankapunkt]

@StorytellerCZ IIRC we have no codeql set up for this repo. We could quickly set this up so @timsun28 could also add the codeql badge to this PRs Readme

[timsun28]

After adding codeql to this repo you can easily get the markdown code following this guide.

Feel free to add the markdown to this pull request or paste it here so I can add it.

[StorytellerCZ]

CodeQL is being setup.

[timsun28]

I've added the GitHub code quality badge to the readme, let me know if there is anything else you would like me to include in this PR that is related to this issue.

[StorytellerCZ]

Made slight adjustments in the contributing file. Just wondering if we need to have the same content in the .github folder and in root.