Add materials on how to setup dev env in CONTRIBUTING guide

[vfdev-5]

🚀 Feature

It would be helpful for the beginners to understand how to setup its development environment and start working on issues. For example, we can base on installing miniconda and setting up a new conda environment.

Idea is to add a small guide here (before Installation section) and provide a link on a complete guide.

Let's also add links to :

• https://docs.conda.io/projects/continuumio-conda/en/latest/user-guide/install/index.html
• https://github.com/firstcontributions/first-contributions

Another point to add is a sentence to prevent modifications of .gitignore as it was decided from the beginning to use locally .git/info/exclude to exclude custom files like: .idea, .vscode etc.

For Hacktoberfest contributors, feel free to ask questions for details if any and say that you would like to tackle the issue.
Please, take a look at CONTRIBUTING guide.

[vfdev-5]

@BanzaiTokyo would you like to tackle this one :)

[BanzaiTokyo]

@vfdev-5 This is definitely doable, but looks time consuming. At the moment I have some other urgent things I need to finish. So it looks like something I could look into in a month or so.

[vfdev-5]

@BanzaiTokyo OK, I see. Let's see if it is still open then you can give it a go as soon as it is possible for you. Otherwise, I can assign it to anyone else :)

[BanzaiTokyo]

sure @vfdev-5 !

[fco-dv]

@vfdev-5 I can give it a try!