R: Vignettes and other documentation

# Vignettes and other documentation

## Vignettes from package 'covidcast'

covidcast::correlation-utils |  | 2. Computing signal correlations | HTML | source |
covidcast::covidcast |  | Get started with covidcast | HTML | source |
covidcast::external-data |  | 4. Combine external data sources and COVIDcast data | HTML | source |
covidcast::multi-signals |  | 3. Manipulating multiple signals | HTML | source |
covidcast::plotting-signals |  | 1. Plotting and mapping signals | HTML | source |