Document how to run solvebio-python in AWS Lambda

[davecap]

To run in lambda, you need to do the following:

• Set SOLVEBIO_LOGFILE environment variable to "" (to avoid creating a log file in the read-only FS)
• Remove any calls to solvebio.login() and set SOLVEBIO_API_HOST and either SOLVEBIO_ACCESS_TOKEN or SOLVEBIO_API_KEY environment variables