Added Multimodal Political Networks book and the goldfish and migraph packages

[BBieri]

Added the following resources:

• Multimudal Political Networks book
  • A methods book applied to political networks by David Knoke, Mario Diani, James Hollway, and Dimitris Christopoulos
• {migraph}
  • A companion R-package for the Multimodal Political Networks book
• {goldfish}
  • A package facilitating the use of Dynamic Network Actor-Oriented Model (DyNAM) for the statistical analysis of coordination networks through time.

Let me know if there is an issue with the way I included the resources. Happy to fix it if so!