Add pypi badge

Author: pgleeson

README.md

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 # Modelspec
 
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+[![Continuous builds](https://github.com/ModECI/modelspec/actions/workflows/ci.yml/badge.svg)](https://github.com/ModECI/modelspec/actions/workflows/ci.yml) [![PyPI](https://img.shields.io/pypi/v/modelspec)](https://pypi.org/project/modelspec/)
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 Functionality for specifying models & enabling automatic serialization (e.g. in JSON and YAML format).
 
 This package is being used by [NeuroMLlite](https://github.com/NeuroML/NeuroMLlite) & [MDF](https://github.com/ModECI/MDF).
 
 
-[![Continuous builds](https://github.com/ModECI/modelspec/actions/workflows/ci.yml/badge.svg)](https://github.com/ModECI/modelspec/actions/workflows/ci.yml)