Integration of VOMS documentation

# Short Description of the issue

Workload manager doc contained few details that could worth to record.
Copying here just to avoid loosing them.

# Summary of proposed changes

#### Install your credentials

```sh
$ mkdir -p $HOME/.globus
$ chmod 700 $HOME/.globus
$ openssl pkcs12 -in $HOME/MyCertificate \ -clcerts -nokeys -out $HOME/.globus/usercert.pem
$ openssl pkcs12 -in $HOME/MyCertificate\ -nocerts -out $HOME/.globus/userkey.pem
$ chmod 600 $HOME/.globus/usercert.pem $HOME/.globus/userkey.pem ```
```