docs: rework the readme (#91)

Re-organize the README and add some more content.

Author: gadomski

README.md

@@ -5,6 +5,48 @@
 Monorepo for Python Satellite Tasking API (STAPI) Specification packages.
 For more, see our [docs](https://stapi-spec.github.io/pystapi/).
 
+> [!WARNING]
+> The STAPI spec, and these packages, are in their early stages of development.
+> There may be large shifts in the spec or these packages' APIs as we work towards a v1.0 release of the spec.
+
+## Packages
+
+There are several related packages in this monorepo:
+
+```mermaid
+graph
+    stapi-pydantic --> pystapi-client --> pystapi-validator
+    stapi-pydantic --> stapi-fastapi
+```
+
+### [stapi-pydantic](./stapi-pydantic/)
+
+[Pydantic](https://docs.pydantic.dev) models for STAPI.
+These models are used to generate the STAPI OpenAPI specification, and so can be considered the source-of-truth for STAPI data structures.
+
+### [stapi-fastapi](./stapi-fastapi/)
+
+A backend-agnostic [FastAPI](https://fastapi.tiangolo.com/) application for serving STAPI endpoints.
+A minimal test implementation is provided in [stapi-fastapi/tests/application.py](stapi-fastapi/tests/application.py).
+Run it like so:
+
+```commandline
+uv run fastapi dev stapi-fastapi/tests/application.py
+```
+
+The app should be accessible at `http://localhost:8000`.
+
+For implementations of **stapi-fastapi** with vendor-specific backends, see repos in the [stapi-fastapi Github organization](https://github.com/stapi-spec?q=stapi-fastapi-&type=all&language=&sort=).
+
+### [pystapi-client](./pystapi-client/)
+
+A Python API and command-line interface (CLI) for working with STAPI servers.
+
+### [pystapi-validator](./pystapi-validator/)
+
+A work-in-progress validator for STAPI APIs.
+Currently not very useful.
+
 ## Development
 
 Get [uv](https://docs.astral.sh/uv/), then:
@@ -34,28 +76,3 @@ source .venv/bin/activate
 ```
 
 See our [contribution guidelines](./CONTRIBUTING.md) for information on contributing any changes, fixes, or features.
-
-## Packages
-
-```mermaid
-graph
-    stapi-pydantic --> pystapi-client --> pystapi-validator
-    stapi-pydantic --> stapi-fastapi
-```
-
-### stapi-fastapi
-
-A minimal test implementation is provided in [stapi-fastapi/tests/application.py](stapi-fastapi/tests/application.py).
-Run it like so:
-
-```commandline
-uv run fastapi dev stapi-fastapi/tests/application.py
-```
-
-The app should be accessible at `http://localhost:8000`.
-
-### pystapi-client
-
-The `pystapi-client` package is a Python client (CLI tool) focused on interfacing with the STAPI specification, specifically with a STAPI server. This is a work in progress.
-
-For more information, see the [README](pystapi-client/README.md).