Update README file to provide examples and metadata

[kstierhoff]

Suggestions for ease of use I have are to flesh out the README a bit, mostly just to have the information you provided me up there. A couple of things that would be especially helpful:

• An example usage to pull data, with the information you provided me above on how to interpret the file names. More or less the R script that you sent me
• Some metadata on the column names

# Example code ----------------------------------
# Install and load pak (library management package)
if (!require("pak")) install.packages("pak")

# Install and load data package from Github -------------------------------
if (!require("atmData")) pkg_install("SWFSC/atmData")
if (!require("tidyverse")) pkg_install("tidyverse")

# Load data from 2024
## Biomass densities
data("nasc_density_2407RL")

# Quick plot of biomass density from 2024
## Sardine density
ggplot(nasc_density_2407RL, aes(long, lat, size = sar.dens, colour = sar.dens)) +
  scale_colour_viridis_c() +
  guides(colour = guide_legend(), size = guide_legend()) +
  geom_point() + 
  facet_wrap(~Region) +
  coord_map() + 
  labs(title = "P. sardine")

## Anchovy density
ggplot(nasc_density_2407RL, aes(long, lat, size = anch.dens, colour = anch.dens)) +
  scale_colour_viridis_c() +
  guides(colour = guide_legend(), size = guide_legend()) +
  geom_point() + 
  facet_wrap(~Region) +
  coord_map() + 
  labs(title = "N. anchovy")

# Reshape data to plot all species
nasc_dens_longer <- nasc_density_2407RL %>% 
  select(lat, long, Region, anch.dens:rher.dens) %>% 
  pivot_longer(anch.dens:rher.dens, names_to = "species", values_to = "density")

## All species density
ggplot(nasc_dens_longer, aes(long, lat, size = density, colour = density)) +
  scale_colour_viridis_c() +
  guides(colour = guide_legend(), size = guide_legend()) +
  geom_point() + 
  facet_grid(Region~species) +
  coord_map()