Update docs and fix typo in Table 1.2 (continuous outcome prediction performance)

[bdwilliamson]

• Add binary outcome specification variable (determines whether IC-50 or IC-80 is used to define binary outcomes) to documentation
• Add combination method (additive or Bliss-Hill) to documentation
• Print correct wording if only IC-80 is requested as a continuous outcome
• Fix typo in metadata that caused something to be printed in first code chunk