Update linux.md

You need to have python2 installed on Arch.

Otherwise you get build ENOENT errors using npm-gyp.
Merge pull request #3950 from avdv/patch-1

Update linux.md
:arrow_up: spell-check@0.43
Upgrade text-buffer to avoid many position translation errors

Refs #3192
Upgrade whitespace to use scoped properties
Upgrade scandal@1.0.3 for isBinary Fix
Give the user settings a priority

Base index 1000
Specs for priority
Upgrade scoped-property-store for priority option
Merge pull request #3944 from atom/bo-defer-config-load

Give scoped user settings a priority
Treat combined characters as paired characters
:memo: Mention combined characters
Add combined characters to spec
:memo: Mention combined characters in spec description
Stored paired characters in width cache

Previously characters were treated individually even when multiple
characters would render as a single character on screen.
:racehorse: Only use String::substr for pair chars
:lipstick:
Access value on token
Add spec for cursor position after pair char
Merge pull request #3953 from atom/ks-support-combining-characters

Support unicode combining characters