📝 Update Readme.

Author: rafalkrupinski

Readme.md

@@ -6,10 +6,18 @@ Python DSL for Web API clients.
 
 http://lapidary.dev/
 
-Also check [lapidary-render](https://github.com/python-lapidary/lapidary-render/),
-a command line program that generates Lapidary clients from OpenAPI.
+## Why
 
-## Usage:
+DRY. Web API clients follow a relatively small set of patterns and writing them is rather repetitive task. Encoding these patterns in form of a DSL library frees its users from implementing the same patterns over and over again.
+
+## How
+
+Lapidary is an internal DSL made of decorators and annotations, that can be used to describe Web APIs similarly to OpenAPI
+([lapidary-render](https://github.com/python-lapidary/lapidary-render/) can convert a large subset of OpenAPI 3.0 to Lapidary).
+
+At runtime, the library interprets user-provided function declarations (without bodies), and makes them behave as declared. If a function accepts parameter of type `X` and returns `Y`, Lapidary will try to convert `X` to HTTP request and the response to `Y`.
+
+### Example:
 
 ```python
 class CatClient(ClientBase):