Update Makefile and add some docs

client/rsh/Makefile

@@ -11,7 +11,7 @@ R := $(R_HOME)/bin/R --slave --no-restore
 LLVM_R := LD_PRELOAD=$(LLVM_LIB) $(R)
 
 .PHONY: all
-all: install
+all: install test benchmark
 
 .PHONY: build
 build:

client/rsh/README.md

@@ -0,0 +1,18 @@
+## Building
+
+```sh
+$ make dependencies
+$ make
+```
+
+For development run:
+
+```sh
+$ make setup
+```
+
+which will create the `compile_commands.json` file for clangd.
+
+You can pass `R_HOME=...` to the make command to specify the R installation to use.
+It is not a bad idea to have a copy of the `../external/R` compiled for debugging.
+To do that you can use the `../../tools/build-gnur.sh` script with `-d` option.