mix: add page (#1714)

pages/common/mix.md

@@ -0,0 +1,23 @@
+# mix
+
+> Mix is a build tool that provides tasks for creating, compiling, and testing Elixir projects, managing its dependencies, and more.
+
+- Execute a particular file:
+
+`mix run {{my_script.exs}}`
+
+- Create a new project:
+
+`mix new {{project_name}}`
+
+- Compile project:
+
+`mix compile`
+
+- Run project tests:
+
+`mix test`
+
+- List all mix commands:
+
+`mix help`