Add html2text in requirements.txt
Add html2text in requirements.txt

When html2text is missing cli.py cannot be executed for install instructions.

CulturePlex/pybossa,OpenNewsLabs/pybossa,proyectos-analizo-info/pybossa-analizo-info,inteligencia-coletiva-lsd/pybossa,harihpr/tweetclickers,jean/pybossa,stefanhahmann/pybossa,Scifabric/pybossa,harihpr/tweetclickers,CulturePlex/pybossa,OpenNewsLabs/pybossa,jean/pybossa,inteligencia-coletiva-lsd/pybossa,CulturePlex/pybossa,PyBossa/pybossa,PyBossa/pybossa,proyectos-analizo-info/pybossa-analizo-info,stefanhahmann/pybossa,geotagx/pybossa,geotagx/pybossa,Scifabric/pybossa,proyectos-analizo-info/pybossa-analizo-info