Update readme

For #32, fixes the issue installation issue: * Installation instructions work and are straightforward, however it would be helpful to add some information about MapBox, and that an API key is needed for some functions. Also note that for some functions, there are packages that will need to be installed separately as they are not installed automatically (i.e., are in `Suggests` - `ceramic`, `ggdist`, etc.)

README.Rmd

@@ -38,6 +38,21 @@ Install the development version from [GitHub](https://github.com/) with:
 remotes::install_github("itsleeds/slopes")
 ```
 
+If you do not already have DEM data and want to make use of the package's ability to download them using the `ceramic` package, install the package with suggested dependencies as follows:
+
+```{r, eval=FALSE}
+# install.packages("remotes")
+remotes::install_github("itsleeds/slopes", dependencies = "Suggests")
+```
+
+Furthermore, you will need to add a MapBox API key to be able to get DEM datasets, by signing up and registering for a key at https://account.mapbox.com/access-tokens/ and then following these steps:
+
+```{r, eval=FALSE}
+usethis::edit_r_environ()
+# Type in (register on the mapbox website):
+MAPBOX_API_KEY=xxxxx
+```
+
 ## Usage
 
 Load the package in the usual way:

README.md

@@ -30,6 +30,26 @@ Install the development version from [GitHub](https://github.com/) with:
 remotes::install_github("itsleeds/slopes")
 ```
 
+If you do not already have DEM data and want to make use of the
+package’s ability to download them using the `ceramic` package, install
+the package with suggested dependencies as follows:
+
+``` r
+# install.packages("remotes")
+remotes::install_github("itsleeds/slopes", dependencies = "Suggests")
+```
+
+Furthermore, you will need to add a MapBox API key to be able to get DEM
+datasets, by signing up and registering for a key at
+<https://account.mapbox.com/access-tokens/> and then following these
+steps:
+
+``` r
+usethis::edit_r_environ()
+# Type in (register on the mapbox website):
+MAPBOX_API_KEY=xxxxx
+```
+
 ## Usage
 
 Load the package in the usual way:
@@ -149,4 +169,4 @@ lisbon_route_3d_auto = slope_3d(lisbon_route)
 plot_slope(lisbon_route_3d_auto)
 ```
 
-<img src="man/figures/README-unnamed-chunk-10-1.png" width="100%" />
+<img src="man/figures/README-unnamed-chunk-12-1.png" width="100%" />