remove rgdal mentions in ReadMe

README.md

@@ -93,16 +93,6 @@ library(remotes)
 install_github("r-spatial/sf", configure.args = "--with-proj-lib=$(brew --prefix)/lib/")
 ```
 
-If you are using `sf` and `rgdal` together, it is necessary to install `rgdal` from source using this configuration:
-
-```r
-install.packages("rgdal", type = "source", configure.args = c("--with-proj-lib=$(brew --prefix)/lib/", "--with-proj-include=$(brew --prefix)/include/"))
-```
-
-Alternatively, [these instructions](https://stat.ethz.ch/pipermail/r-sig-mac/2017-June/012429.html) explain how to install gdal using kyngchaos frameworks.
-
-For Mac OS 11 Big Sur source install instruction, see [here](https://github.com/r-spatial/sf/issues/1536#issuecomment-727342736)
-
 ### Linux
 
 For Unix-alikes, GDAL (>= 2.0.1), GEOS (>= 3.4.0) and Proj.4 (>= 4.8.0) are required.