add(arch linux install)

[justleoo]

i added the option to use pacman, which works on distros like arch linux, and arch linux based distros, i already sent it adding this way of installation in denoland/deno. :heart:

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[rojvv]

@justleoo please run deno fmt to fix formatting issues.

[justleoo]

@justleoo please run deno fmt to fix formatting issues.

done