Update README to reflect #17 and #14 [no ci]

README.Rmd

@@ -124,7 +124,15 @@ loaded via a namespace (and not attached):
 [37] crayon_1.3.4    
 ```
 
-## Using alternative Rocker images
+### Caching R packages
+
+One can also cache (or archive) the R packages from CRAN at the time `dockerize` is executed. The cached R packages will then transfer to the container. Please note that system requirements (i.e. `deb` packages) are not cached.
+
+```r
+dockerize(graph, "~/rocker_test", cache = TRUE)
+```
+
+### Using alternative Rocker images
 
 One can also select other Rocker versioned images: `rstudio`, `tidyverse`, `verse`, `geospatial`.
 
@@ -142,6 +150,15 @@ sudo docker run -p 8787:8787 -e PASSWORD=abc123 --rm --name "grantest" -ti gran
 
 With any browser, go to: `local:8787`. The default username is `rstudio`, password is as specified.
 
+## Recreate the computational environment for R < 3.1.0
+
+`gran` can still be used to recreate computational environments for R < 3.1.0. The Dockerfile generated is based on Debian Woody (3.0) and the requested version of R is compiled from source. As of writing, this method works for R < 3.1.0 but not R < 2.1.0. The `image` parameter is ignored in this case.
+
+```r
+gran_rio <- resolve("rio", snapshot_date = "2013-08-28") ## R 3.0.1
+dockerize(gran_rio, output_dir = "~/old_renviron")
+```
+
 ## Acknowledgment
 
 The logo of gran is a remix of [this](https://commons.wikimedia.org/wiki/File:Flag_of_the_Canary_Islands.svg) public domain image. The two dogs should be *Presa Canario*, the native dog breed on the islands of Gran Canaria and Tenerife.

README.md

@@ -144,7 +144,18 @@ loaded via a namespace (and not attached):
 [37] crayon_1.3.4    
 ```
 
-## Using alternative Rocker images
+### Caching R packages
+
+One can also cache (or archive) the R packages from CRAN at the time
+`dockerize` is executed. The cached R packages will then transfer to the
+container. Please note that system requirements (i.e. `deb` packages)
+are not cached.
+
+``` r
+dockerize(graph, "~/rocker_test", cache = TRUE)
+```
+
+### Using alternative Rocker images
 
 One can also select other Rocker versioned images: `rstudio`,
 `tidyverse`, `verse`, `geospatial`.
@@ -165,6 +176,19 @@ sudo docker run -p 8787:8787 -e PASSWORD=abc123 --rm --name "grantest" -ti gran
 With any browser, go to: `local:8787`. The default username is
 `rstudio`, password is as specified.
 
+## Recreate the computational environment for R \< 3.1.0
+
+`gran` can still be used to recreate computational environments for R \<
+3.1.0. The Dockerfile generated is based on Debian Woody (3.0) and the
+requested version of R is compiled from source. As of writing, this
+method works for R \< 3.1.0 but not R \< 2.1.0. The `image` parameter is
+ignored in this case.
+
+``` r
+gran_rio <- resolve("rio", snapshot_date = "2013-08-28") ## R 3.0.1
+dockerize(gran_rio, output_dir = "~/old_renviron")
+```
+
 ## Acknowledgment
 
 The logo of gran is a remix of