Add Rstudio usage instructions

[josemunozc]

$ module purge
$ module load rstudio-server
$ srun -p htc -n 1 --account=scw1001 rstudio-server
(You will need to wait for a node to become available)
This will print out a server address and a password to access the site.
Then to connect to Hawk again using ssh, for example via the command line
$ ssh -L8787: hawklogin.cf.ac.uk

e.g.
$ srun -p htc -n 1 --account=scw1001 rstudio-server
INFO: Server address is: ccs2105:8787
INFO: Password to access site is: iZiemCGx7GDxV
Then I would type on my laptop/desktop:
$ ssh -L8787:ccs2105:8787 hawklogin.cf.ac.uk
THen with a browser on the laptop/desktop I can goto:
http://localhost:8787
Then type in my SCW username and the password generated above.