SAN FRANCISCO (Reuters) - Facebook Inc will add banks in coming weeks to help underwrite its initial public offering, two sources familiar with its plans said on Friday. Deutsche Bank, Credit Suisse and Citigroup are among the banks that will likely be added, said the sources, who requested anonymity because they were not authorized to speak publicly on the matter. Last September, Facebook increased its credit line to $2.5 billion. One of the sources said that the credit line may be increased to about $5 billion in the future. In February 2011, Facebook set up a $1. ...