update #1 - existing troubleshooting

Existing troubleshooting documentation all bring at the same place.

docs/general-troubleshooting.md

@@ -1,2 +1,32 @@
 # Common errors and troubleshooting
 
+## Recommandation
+If you think you have a problem with your XOA, start by typing`xoa check`command in your terminal:   
+
+```
+$ xoa check
+✔ Node version
+✔ Disk space for /var
+✔ Disk space for /
+✔ XOA version
+✔ xo-server config syntax
+✔ Appliance registration
+✔ Internet connectivity
+```  
+If the result you have is completely different than that, or if error messages are display, lost packets, etc., you have, indeed, a problem. The next step should be to check in this document if there is an existing troubleshooting for the problem you have. 
+
+> You can also access the log by using this command: `$ tail -f /var/log/syslog` ([learn more](https://xen-orchestra.com/docs/logs.html))
+
+## General
+
+* [Empty page after login](https://xen-orchestra.com/docs/troubleshooting.html#empty-page-after-login)
+* [Network issues](https://xen-orchestra.com/docs/troubleshooting.html#network-issues)
+* [Out of memory](https://xen-orchestra.com/docs/troubleshooting.html#memory)
+* [Transparent proxy and updater](https://xen-orchestra.com/docs/troubleshooting.html#behind-a-transparent-proxy)
+* [SSL self-signed certificate expired](https://xen-orchestra.com/docs/troubleshooting.html#updating-ssl-self-signed-certificate)
+* [User authentication](https://xen-orchestra.com/docs/authentication.html#debugging)
+
+## Backup troubleshooting
+
+* [Unhealthy VDI chain](https://xen-orchestra.com/docs/backup_troubleshooting.html#unhealthy-vdi-chain)
+* [SR_backend_failure_44](https://xen-orchestra.com/docs/backup_troubleshooting.html#srbackendfailure44-insufficient-space)