Add some information on services running on shadow

Author: rerpha

doc/systems/Shadow.md

@@ -0,0 +1,22 @@
+# Shadow
+
+Shadow is a Linux machine which hosts various services. Credentials are in Keeper. 
+
+## Apache
+
+Apache is running as the main http server, it proxies requests running to other services ie. Jenkins on shadow.
+
+Configuration is located at `/etc/httpd/conf.d/`.
+
+## Jenkins
+
+Shadow hosts the [Jenkins instance.](https://epics-jenkins.isis.rl.ac.uk/) and is the built-in node.   
+
+This runs as a `systemd` service called `jenkins`, its configuration is stored in `/isis2/jenkins/instances/epics/`.
+
+## Site-mirrored Wikis
+
+These are currently being built by Github actions, Shadow executes periodic cron jobs (run `sudo su - isisupdate` then `crontab -e` to see these) which pull the `gh-pages` branches of the Github wikis.
+
+The cron jobs run `/isis/scripts/update_x` where `x` is the name of the wiki.
+

doc/systems/Webserver.md

@@ -22,3 +22,7 @@ If a new server is setup, then ciphers and old TLS versions may need to be disab
 ## NDAEXTWEB4
 
 NDAEXTWEB4 is similar in that it also runs on the Hyper-V cluster. This currently hosts the [PVWS](/webdashboard/PVWS) which is a PVWS instance for the IBEX web dashboard. 
+
+## Shadow
+    
+Some web services run on Shadow - see [here](/systems/Shadow) for more information.