add installation instructions from romancal

README.md

@@ -9,14 +9,87 @@ This is a repository for the Roman Attribute Dictionary
 
 ## Installation
 
-To install the latest `rad` release
+The easiest way to install the latest `rad` release into a fresh virtualenv or conda environment is
 
     pip install rad
 
-To install the latest code from the repository
+### Detailed Installation
 
-    pip install git+https://github.com/spacetelescope/rad.git
+The `rad` package can be installed into a virtualenv or conda environment via `pip`. We recommend that for each
+installation you start by creating a fresh environment that only has Python installed and then install the `rad`
+package and its dependencies into that bare environment. If using conda environments, first make sure you have a recent
+version of Anaconda or Miniconda installed. If desired, you can create multiple environments to allow for switching
+between different versions of the `rad` package (e.g. a released version versus the current development version).
 
-To use the library
+In all cases, the installation is generally a 3-step process:
+
+* Create a conda environment
+* Activate that environment
+* Install the desired version of the `rad` package into that environment
+
+Details are given below on how to do this for different types of installations, including tagged releases, DMS builds
+used in operations, and development versions. Remember that all conda operations must be done from within a bash shell.
+
+### Installing latest releases
+
+You can install the latest released version via `pip`. From a bash shell:
+
+    conda create -n <env_name> python
+    conda activate <env_name>
+    pip install rad
+
+> **Note**\
+> Alternatively, you can also use `virtualenv` to create an environment;
+> however, this installation method is not supported by STScI if you encounter issues.
+
+You can also install a specific version (from `rad 0.1.0` onward):
+
+    conda create -n <env_name> python
+    conda activate <env_name>
+    pip install rad==0.5.0
+
+### Installing the development version from Github
+
+You can install the latest development version (not as well tested) from the Github main branch:
+
+    conda create -n <env_name> python
+    conda activate <env_name>
+    pip install git+https://github.com/spacetelescope/rad
+
+### Installing for Developers
+
+If you want to be able to work on and test the source code with the `rad` package, the high-level procedure to do
+this is to first create a conda environment using the same procedures outlined above, but then install your personal
+copy of the code overtop of the original code in that environment. Again, this should be done in a separate conda
+environment from any existing environments that you may have already installed with released versions of the `rad`
+package.
+
+As usual, the first two steps are to create and activate an environment:
+
+    conda create -n <env_name> python
+    conda activate <env_name>
+
+To install your own copy of the code into that environment, you first need to fork and clone the `rad` repo:
+
+    cd <where you want to put the repo>
+    git clone https://github.com/spacetelescope/rad
+    cd rad
+
+> **Note**\
+> Installing via `setup.py` (`python setup.py install`, `python setup.py develop`, etc.) is deprecated and does not work.
+
+Install from your local checked-out copy as an "editable" install:
+
+    pip install -e .
+
+If you want to run the unit or regression tests and/or build the docs, you can make sure those dependencies are
+installed too:
+
+    pip install -e ".[test]"
+    pip install -e ".[docs]"
+    pip install -e ".[test,docs]"
+
+Need other useful packages in your development environment?
+
+    pip install ipython pytest-xdist
 
-    >>> import rad