META - Update migrated documentation

[pavithraes]

Documentation was recently migrated into Docusaurus and new structure. This issue tracks updating various pages:

### conda-store
- [x] Introduction (update with learning paths) - #724
- [x] How to - Standalone install - #724
- [ ] How to - Docker installation
- [ ] How to - Kubernetes installation
- [ ] #727 (how-to)
- [ ] Tutorials - Using conda-store CLI
- [ ] Tutorials - Using conda-store as shebang (move from how-to)
- [x] Explanations - #726
- [ ] References - Architecture docs

### conda-store-ui
- [ ] Introduction (update with learning paths)
- [ ] Explanations - UI Components
- [ ] https://github.com/conda-incubator/conda-store/issues/780

### Community
- [ ] Contributing guidelines - #763
- [ ] https://github.com/conda-incubator/conda-store/issues/753

[pavithraes]

Note to add the following section in conda-store-UI's how-to's around admin settings:

This was originally documented with artifacts, but removed in #726

#### Existing Deployments

conda-store saves environment settings and doesn't automatically update them on
startup (see `CondaStore.ensure_settings`). Existing deployments need to
manually enable installer builds via the admin interface. This can be done by
going to `<CondaStoreServer.url_prefix>/admin/setting/<namespace>/<env>/` (or
clicking on the `Settings` button on the environment page) and adding
`"CONSTRUCTOR_INSTALLER"` to `build_artifacts`.