Add introductory text for models in documentation

[jessica-mitchell]

This PR adds introductory text to explain a bit about models in NEST.

@clinssen @pnbabu I added a section on NESTML that is copied from your docs, please comment if you have some other text you would like better.

There is a table of terms used in model names along with commonly used terms in literature. It's incomplete and in need of a model expert to help fill it out.

https://nest-test.readthedocs.io/en/add-intro-models/models/models-main.html

[clinssen]

Just some initial ideas!

[jessica-mitchell]

@pnbabu @clinssen Thanks for your comments, I applied your suggestions, and I created a page on the installation for installing NEST with NESTML - it doesnt got into much detail. I think most of the information should be kept in your docs - the only thing that might be necessary imo, is if there is any additional setup to get NESTML to work with NEST aside from having them both installed. Also note that in #2289 I added a link to the global toc for NESTML.

[terhorstd]

@jessica-mitchell, the last merges caused a tiny conflict, could you resolve those? This seems otherwise almost ready to go… don't hesitate to re-request review when appropriate :)

[jessica-mitchell]

@terhorstd I'm still looking for someone to review the table I created that compares NEST terms with commonly used ones in research (like CUBA and psc for current-based)

[pnbabu]

Some additional comments

• In the Lecturer installation instructions page, under the Docker image section, could you also mention that NESTML is included within the NEST docker image?
• Can the nest::docs logo in the header be made clickable so that the user can navigate to the home page by clicking that?
• The Contents on the right-hand side for all pages contain a link to Show Source . Is this kept deliberately?

[jessica-mitchell]

Some additional comments

* In the `Lecturer installation instructions` page, under the `Docker image` section, could you also mention that NESTML is included within the NEST docker image?

Done

* Can the `nest::docs` logo in the header be made clickable so that the user can navigate to the home page by clicking that?

Yes, but that's for another PR.

* The `Contents` on the right-hand side for all pages contain a link to `Show Source` . Is this kept deliberately?

That is the default for the theme and I dont see anything wrong with it. If you think this needs to change then please create an issue for it. I don't want to add a bunch more irrelevant things to this PR or it will never be merged. The focus is on the model intro page.

[clinssen]

Thanks!

[akorgor]

This already looks great and useful! :) I added some minor to medium suggestions.

[jessica-mitchell]

@akorgor thanks for your feedback, I think I addressed all the points you raised, please resolve the remaining conversations and approve if you are satisfied

[jessica-mitchell]

@akorgor sorry about that! Now, I think I got them all - removed the bullet text

[jessica-mitchell]

@akorgor I have added your suggestion, thanks! Can you take one final look and approve if you're happy?