Improve getting started documentation for developers

[DanielleRameau]

As a developer I want to see a list of steps I need to take in order to get the SLDS working with my theme.

• GitHub token setup so you can npm add the NPM packages
• What to do to get the SLDS colors & fonts of my CFA to work
• What to do to get a simple <sl-button> to show up in my web application (Angular?)

Clear steps on what you need to add to .npmrc or .yarnrc.yml:

@sl-design-system:registry=https://npm.pkg.github.com/
//npm.pkg.github.com/:_authToken=XXXXXXXXX

(in the case of .npmrc)

### User stories
- [x] Angular + Svelte documentation
- [x] What do I need to do to let it work in my angular application?
- [x] Add clear steps on getting started page (step 1,2,3)
- [x] Why is my font not showing up?
- [x] Mention SSR
- [x] Mention how to switch between light and dark (is dark mode is available)
- [x] How to create a GitHub Token: should be classic & should have `read_packages` privilege at least
- [x] How to use the shared token within Bitbucket Pipelines
- [x] What Angular versions we support

[anna-lach]

Maybe also make some research about preparing bundle for Angular of our npm packages?

[Diaan]

https://sanoma-my.sharepoint.com/:w:/p/diana_broeders/ETWhVQXL_zNEsDyvMkg1U0YBErW7p4ww-NPFo5K8onxMfg?e=mJDQJi The current how to annotated with changes