refactor(kb): give linux-specific articles their own section

knowledge base/linux/alpine.md

@@ -0,0 +1,30 @@
+# Alpine
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+
+## TL;DR
+
+```sh
+# Create users.
+adduser 'somebody'
+adduser -DHS -G 'docker' 'docker'
+
+# Create groups.
+addgroup 'new-group'
+
+# Add users to groups.
+addgroup 'nobody' 'docker'
+```
+
+## Further readings
+
+- [APK]
+
+<!--
+  Reference
+  ═╬═Time══
+  -->
+
+<!-- Knowledge base -->
+[apk]: ../apk.md