Updates to main README

Author: duckontheweb

README.md

@@ -1,29 +1,39 @@
 ## PySTAC
-![Build Status](https://github.com/stac-utils/pystac/workflows/CI/badge.svg?branch=develop)
+![Build Status](https://github.com/stac-utils/pystac/workflows/CI/badge.svg?branch=main)
 [![PyPI version](https://badge.fury.io/py/pystac.svg)](https://badge.fury.io/py/pystac)
 [![Documentation](https://readthedocs.org/projects/pystac/badge/?version=latest)](https://pystac.readthedocs.io/en/latest/)
 [![codecov](https://codecov.io/gh/stac-utils/pystac/branch/main/graph/badge.svg)](https://codecov.io/gh/stac-utils/pystac)
-[![Gitter chat](https://badges.gitter.im/azavea/pystac.svg)](https://gitter.im/azavea/pystac)
+
 [![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://opensource.org/licenses/Apache-2.0)
 
 PySTAC is a library for working with [SpatialTemporal Asset Catalog](https://stacspec.org) in Python 3.
 
 ## Installation
 
-PySTAC has a single dependency (`python-dateutil`).
+PySTAC has a single required dependency (`python-dateutil`).
 PySTAC can be installed from pip or the source repository.
 
 ```bash
 > pip install pystac
 ```
 
-if you'd like to enable the validation feature utilizing the [jsonschema](https://pypi.org/project/jsonschema/) project, install with the optional `validation` requirements:
+If you would like to enable the validation feature utilizing the
+[jsonschema](https://pypi.org/project/jsonschema/) project, install with the optional
+`validation` requirements: 
 
 
 ```bash
 > pip install pystac[validation]
 ```
 
+If you would like to use the [`orjson`](https://pypi.org/project/orjson/) instead of the
+standard `json` library for JSON serialization/deserialization, install with the
+optional `orjson` requirements:
+
+```bash
+> pip install pystac[orjson]
+```
+
 From source repository:
 
 ```bash
@@ -34,28 +44,31 @@ From source repository:
 
 
 #### Versions
-To install a specific versions of STAC, install the matching version of pystac.
-
-```bash
-> pip install pystac==0.5.*
-```
-
-The table below shows the corresponding versions between pystac and STAC:
+To install a version of PySTAC that works with a specific versions of the STAC
+specification, install the matching version of PySTAC from the following table.
 
-| pystac | STAC  |
+| PySTAC | STAC  |
 | ------ | ----- |
 | 1.x    | 1.0.x |
 | 0.5.x  | 1.0.0-beta.* |
 | 0.4.x  | 0.9.x |
 | 0.3.x  | 0.8.x |
 
+For instance, to work with STAC v0.9.x:
+
+```bash
+pip install pystac==0.4.0
+```
+
+STAC spec versions below 0.8 are not supported by PySTAC.
+
 ## Documentation
 
 See the [documentation page](https://pystac.readthedocs.io/en/latest/) for the latest docs.
 
 ## Developing
 
-See [contributing docs](docs/contributing.rst)
+See [contributing docs](docs/contributing.rst) for details on contributing to this project.
 
 ## Running the quickstart and tutorials