update readme

README.md

 # alapur
 
-## Prerequisite
-
-Install the "remotes" R-package
-```R
-source("https://raw.githubusercontent.com/r-lib/remotes/master/install-github.R")$value("r-lib/remotes")
-```
 
 ## Installation
 
 ```R
-library("remotes")
-remotes::install_git("git@git.nilu.no:alapu/alapur.git")
+library("devtools")
+devtools::install_git("git@git.nilu.no:alapu/alapur.git")
 ```