Update installation instructions for the new conda-forge packages and…

… other changes in our packaging infra (napari#202)

# Description
Consolidated docs update for info about:

* conda-forge/napari-feedstock#48
* napari/packaging#75
* napari/packaging#77


## Type of change
<!-- Please delete options that are not relevant. -->
- [X] Fixes or improves existing content

# References
* conda-forge/napari-feedstock#48
* napari/packaging#75
* napari/packaging#77

## Final checklist:
- [x] My PR is the minimum possible work for the desired functionality

---------

Co-authored-by: Peter Sobolewski <76622105+psobolewskiPhD@users.noreply.github.com>

docs/developers/packaging.md

@@ -145,11 +145,11 @@ signing_certificate: certificate.pfx  # path to signing certificate
 
 The main OS-agnostic keys are:
 
-* `channels`: where the packages will be downloaded from.
-  We mainly rely on `conda-forge` for this, where `napari` is published.
-  However, we also have `napari/label/bundle_tools_2`, where we store our `constructor` stack forks (more on this later).
-  In nightly installers, we locally build our own development packages for `conda`, without resorting to `conda-forge`.
-  To make use of those (which are eventually published to `napari/label/nightly`),
+* `channels`: where the packages will be downloaded from. 
+  We mainly rely on `conda-forge` for this, where `napari` is published. 
+  However, we also have `napari/label/bundle_tools_3`, where we store our `constructor` stack forks (more on this later). 
+  In nightly installers, we locally build our own development packages for `conda`, without resorting to `conda-forge`. 
+  To make use of those (which are eventually published to `napari/label/nightly`), 
   we unpack the GitHub Actions artifact in a specific location that `constructor` recognizes as a _local_ channel once indexed.
 * {{ '`extra_envs> napari-NAPARI_VER`'.replace('NAPARI_VER', napari_version) }}: the environment that will actually contain the napari installation.
   In this key, you will find `specs`, which lists the conda packages to be installed in that environment.