docs: fix outdated setup guidance (#1481)

Author: Anber

CONTRIBUTING.md

@@ -18,10 +18,10 @@ The core team works directly on GitHub and all work is public.
 
 1. Run `pnpm bootstrap` to setup the development environment.
 
-1. When working on the code, you can use the watch mode to watch and compiles changed files:
+1. When working on a package, you can use that package's watch script to watch and compile changed files:
 
    ```sh
-   pnpm watch
+   pnpm --filter @linaria/react watch
    ```
 
 1. If you've added code that should be tested, add tests.

docs/ATOMIC_CSS.md

@@ -28,9 +28,7 @@ Atomic CSS is a way of writing CSS such that each CSS rule has exactly one decla
 
 ## Usage in Linaria
 
-Atomic styles can be enabled in the linaria config by providing an `atomizer` function (see [configuration](./CONFIGURATION.md) for details).
-
-Once enabled, it is possible to write atomic styles by importing the `css` template literal from `@linaria/atomic`:
+Atomic styles do not require a separate config option. Use them by importing the `css` template literal from `@linaria/atomic`:
 
 ```tsx
 import { cx } from '@linaria/core';

docs/CONFIGURATION.md

@@ -122,7 +122,7 @@ module.exports = {
   `;
   ```
 
-- `classNameSlug: string | ((hash: string, title: string, args: ClassNameSlugVars) => string)` (default: `default`):
+- `classNameSlug: string | ((hash: string, title: string, args: ClassNameSlugVars) => string)` (default: generated from the class hash, with the display name prefix when `displayName` is enabled):
 
   Using this will provide an interface to customize the output of the CSS class name. Example:
 
@@ -154,13 +154,13 @@ module.exports = {
   - `hash`: The hash of the content.
   - `title`: The name of the class.
 
-- `variableNameSlug: string | ((context: IVariableContext) => string)` (default: `default`):
+- `variableNameSlug: string | ((context: IVariableContext) => string)` (default: Linaria-generated variable id):
 
   Using this will provide an interface to customize the output of the CSS variable name. Example:
 
       variableNameSlug: '[componentName]-[valueSlug]-[index]',
 
-  Would generate a variable name such as `--Title-absdjfsdf-0` instead of the `@react/styled`'s default `--absdjfsdf-0`.
+  Would generate a variable name such as `--Title-absdjfsdf-0` instead of the `@linaria/react`'s default `--absdjfsdf-0`.
 
   You may also use a function to define the slug. The function will be evaluated at build time and must return a string: