Update iridis.md

howTo/iridis.md

 # How to use the UoS Iridis HPC
 
 HPC = [High Performance Computer](https://www.southampton.ac.uk/isolutions/staff/iridis.page). Lots of memory, lots of processors, good if you can parallelise your code. Can you?
+
+## Which Iridis?
+
+We have:
+
+ * Iridis 4: https://hpc.soton.ac.uk/redmine/projects/iridis-4-support/wiki
+ * Iridis 5: https://hpc.soton.ac.uk/redmine/projects/iridis-5-support/wiki
+
+5 is newer, bigger & better etc etc but new projects start on 4 and, presumably when you prove you need 5, you can transfer.
+
+## How to access
+Fill in the form on the [iridis page](https://www.southampton.ac.uk/isolutions/staff/iridis.page).
+
+## How to login
+
+OK, so you are going to need to [get a bit friendly with unix](https://www.dummies.com/computers/operating-systems/unix/) because the Iridis service runs unix (linux). In general you will be interacting with it using a command line tool like terminal/console etc. Back to the good old days. 
+
+You can, possibly, get iridis to open an Xwindow on your PC nut that requires fancy ssh tunneling and stuff.
+
+Assuming you want iridis 4 to start with you can login to any of:
+
+ * iridis4_a.soton.ac.uk
+ * iridis4_b.soton.ac.uk
+ * iridis4_c.soton.ac.uk
+
+
+To do this:
+
+ * make sure you are running the UoS vpn
+ * open a terminal/console window on your desktop
+ * type `ssh YourUsername@iridis4_a.soton.ac.uk` (or which ever you want). & hit return. YourUsername = your UoS username obvs
+ * type `yes` to the fingerprint question (DO NOT PANIC!). This should only happen the first time you do this
+ * type your UoS password & hit return
+ * you're in!