Update README.md

• added default port to example endpoint (proxmox.endpoint)
• added note on the need to add @pam to get access to the API, changed example values to make it clearer we're talking about the Proxmox user
• changed the filename in proxmox.os_template to the template link to in this file
Merge pull request #10 from nbrogi/master

Update README.md
• added default port to example endpoint (proxmox.endpoint)
• added note on the need to add @pam to get access to the API, changed example values to make it clearer we're talking about the Proxmox user
• changed the filename in proxmox.os_template to the template link to in this file