Added First Boot section. Added Language Selection page and media.

content/first-boot.md

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+# First Boot
+
+When you first boot up your new Solus system, you will be setting up your language and keyboard settings, your user account, and network settings.
+
+<!-- Reference first-boot/* contents. -->

content/first-boot/language-selection.md

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+## Language Selection
+
+Select the language to use on your computer. *You can add more later.*
+
+![Select your language](../images/first-boot/language-selection.png)
+
+If the language is listed like above, click it. Otherwise click the ⋮ for more options. Then proceed by clicking the Next button in the top right corner.