Auto merge of #19867 - pandusonu2:ReadMeFix, r=mbrubeck

Update README.md to fix font requirements for Arch Linux

The current specifications for installation of Servo in Arch Linux fails to run due to requirement of fonts.

The fix is just to include the required package in the required dependencies list in README.md.

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I added the required font package for Arch Linux in the README file. This is in accordance with the comments on the bug #12107, which deals with similar requirements for Gentoo
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- [ ] These changes fix #__ (github issue number if applicable).

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README.md

@@ -119,7 +119,7 @@ sudo zypper install libX11-devel libexpat-devel libbz2-devel Mesa-libEGL-devel M
 #### On Arch Linux
 
 ``` sh
-sudo pacman -S --needed base-devel git python2 python2-virtualenv python2-pip mesa cmake bzip2 libxmu glu pkg-config
+sudo pacman -S --needed base-devel git python2 python2-virtualenv python2-pip mesa cmake bzip2 libxmu glu pkg-config ttf-fira-sans
 ```
 #### On Gentoo Linux