add usage examples [WIP]

Author: ctoney

README.Rmd

@@ -84,7 +84,7 @@ Helper functions are provided to facilitate analyzing FIA tree lists as Spatial
 X <- create_fia_ppp(plantation)
 summary(X)
 
-plot(X, pch = 16, main = "Loblolly pine plantation")
+plot(X, pch = 16, background = "gray90", main = "Loblolly pine plantation")
 
 # compute Ripley's K-function applying isotropic edge correction
 K <- spatstat.explore::Kest(X, rmax = 12, correction = "isotropic")

README.md

@@ -164,7 +164,7 @@ summary(X)
 #> Unit of length: 1 foot
 #> Fraction of frame area: 0.124
 
-plot(X, pch = 16, main = "Loblolly pine plantation")
+plot(X, pch = 16, background = "gray90", main = "Loblolly pine plantation")
 ```
 
 <img src="man/figures/README-spatstat-explore-1.png" alt="" width="70%" />