docs: add some WIP docs files

Author: NoNameProvided

docs/SUMMARY.md

@@ -1,3 +1,4 @@
 # Table of contents
 
 - [Getting Started](pages/01-getting-started.md)
+- [Basic usage](pages/02-basis-usage.md)

docs/pages/02-basic-usage.md

@@ -0,0 +1,20 @@
+# Basic usage
+
+There are two main exported functions what can be used for transformations:
+
+- `plainToClass` - transforms a plain object to an instance of the specified class constructor
+- `classToPlain` - transforms a _known_ class instance to a plain object
+
+Both function transforms the source object to the target via applying the metadata registered by the decorators on
+the class definition. The four main decorators are:
+
+- `@Expose` specifies how expose the given property on the plain object
+- `@Exclude` marks the property as skipped, so it won't show up in the transformation
+- `@Transform` allows specifying a custom transformation on the property via a custom handler
+- `@Type` decorator explicitly sets the type of the property, during the transformation `class-transformer` will attempt
+  to create an instance of the specified type
+
+You must always decorate all your properties with an `@Expose` or `@Exclude` decorator.
+
+> **NOTE:** It's important to remember `class-transformer` will call the target type with am empty constructor, so if
+> you are using a type what requires special setup, you need to use a `@Transform` decorator and create the instance yourself.