Use requirements.txt inside setup.py (#711)

Enhancement proposal. It would be great if `pip install git+https://github.com/bigscience-workshop/promptsource` would install the package dependencies. I faced this inconvenience when installing T0 repository in a clean environment. T0 only specifies `promptsource` as a dependency and because the `requirements.txt` in promptsource are not propagated into its `setup.py`, the package is installed without `sentencepiese` and `jinja2`.

Author: Guitaricet

setup.py

@@ -3,13 +3,17 @@
 with open('README.md') as readme_file:
  readme = readme_file.read()
 
+with open('requirements.txt') as requirements_file:
+ requirements = requirements_file.read().split('\n')
+
 setup(
  name='promptsource',
  version='0.1.0',
  url='https://github.com/bigscience-workshop/promptsource.git',
  author='Multiple Authors',
  author_email='xxx',
  python_requires='>=3.7, <3.8',
+ install_requires=requirements,
  classifiers=[
  'Development Status :: 2 - Pre-Alpha',
  'Intended Audience :: Developers',