Added Arch Linux logo to OS icons

(As of this commit, the logo is not yet used in the LibreNMS web UI.)

Adapted from https://sources.archlinux.org/other/artwork/archlinux-logo-dark-scalable.svg.

According to an email by Aaron Griffin, use of the logo in LibreNMS is
permitted as long as no commercial interests are pursued and the TM symbol is
included in the logo:

  On 22.09.2015 18:17, Nils Steinger wrote:
  > To Whom It May Concern:
  >
  > I'm a new user of the LibreNMS network monitoring system (an Open Source
  > fork of Observium) [1].
  > LibreNMS has inherited a number of logos from Observium that are
  > displayed in the list of monitored hosts to show what *nix/Linux
  > distribution they are running.
  >
  > Would it be possible to add a 32×32 or 48×48 px version of the Arch
  > Linux logo (like the one attached to this email) to LibreNMS?
  >
  > LibreNMS has no commercial interests, but I'm not sure whether the Arch
  > Linux Trademark Policy allows creating derivatives of the logo and
  > including them in software distributions, hence this inquiry.
  >
  > Best Regards,
  > Nils Steinger
  >
  >
  > [1]: https://github.com/librenms/librenms

  On 22.09.2015 19:54, Aaron Griffin wrote:
  > This is an acceptable use of the logo - the only thing we ask is that you
  > maintain the TM symbol on the logo.

html/images/os/archlinux.svg

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