Update graphical remote access info

[nullnik-0]

The info about graphical remote access options in computing-resources/neuropoly/README.md is outdated. Notably:

• Instructions provided for VNC are no longer operable and should be removed.
• XRDP is now available on Linux servers, as documented within this issue. However, this not documented anywhere on the intranet.

Updates that should be made to docs:

• Add general info about XRDP.
• Document remmina and freerdp clients for Linux users.
• Test freerdp client on macOS host.
• Document freerdp client for macOS users.
• Document standard RDP connection for Windows users.
• Have another Linux user review Windows docs, and confirm ability to make a working connection.
• Have a macOS user review macOS docs, and confirm ability to make a working connection.
• Have a Windows user fact check Windows docs, and confirm ability to make working connection.
• Remove outdated VNC info.