Update README.md

README.md

@@ -33,6 +33,12 @@ You must install the following softwares and packages :
 - [R Version 3.2.3](https://cran.r-project.org/)
     - [R-package]ggplot2 `install.packages("ggplot2")`
     - [R-package]rgeos `install.packages("rgeos")`
+        - or alternatively
+        ```
+        packageRgeosURL="https://cran.r-project.org/src/contrib/Archive/rgeos/rgeos_0.3-26.tar.gz"
+        install.packages(packageRgeosURL, type="source")
+        ```
+install.packages(packageRgeosURL, type="source")
     - [R-package]rgdal `install.packages("rgdal")` it may require to install `libgdal-dev`
     - [R-package]nodiv `install.packages("nodiv")`
     - [R-package]raster `install.packages("raster")`