postcss: add page (#1969)

pages/common/postcss.md

@@ -0,0 +1,35 @@
+# postcss
+
+> PostCSS is a tool for transforming styles with JS plugins.
+
+- Parse and transform a CSS file:
+
+`postcss {{path/to/file}}`
+
+- Parse and transform a CSS file and output to a specific file:
+
+`postcss {{path/to/file}} --output {{path/to/file}}`
+
+- Parse and transform a CSS file and output to a specific directory:
+
+`postcss {{path/to/file}} --dir {{path/to/directory}}`
+
+- Parse and transform a CSS file in-place:
+
+`postcss {{path/to/file}} --replace`
+
+- Specify a custom PostCSS parser:
+
+`postcss {{path/to/file}} --parser {{parser}}`
+
+- Specify a custom PostCSS syntax:
+
+`postcss {{path/to/file}} --syntax {{syntax}}`
+
+- Watch for changes to a CSS file:
+
+`postcss {{path/to/file}} --watch`
+
+- Display available options and examples:
+
+`postcss --help`