Add readme (#5)

* add readme written by ChatGPT

* human corrections

* review corrections

* remove ordered collection limitation

Author: JanTvrdik

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2024 Bedabox, LLC dba ShipMonk
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -0,0 +1,80 @@
+# Doctrine Entity Preloader
+
+`shipmonk/doctrine-entity-preloader` is a PHP library designed to tackle the n+1 query problem in Doctrine ORM by efficiently preloading related entities. This library offers a flexible and powerful way to optimize database access patterns, especially in cases with complex entity relationships.
+
+- 🚀 **Performance Boost:** Minimizes n+1 issues by preloading related entities with **constant number of queries**.
+- 🔄 **Flexible:** Supports all associations: `#[OneToOne]`, `#[OneToMany]`, `#[ManyToOne]`, and `#[ManyToMany]`.
+- 💡 **Easy Integration:** Simple to integrate with your existing Doctrine setup.
+
+## Installation
+
+To install the library, use Composer:
+
+```sh
+composer require shipmonk/doctrine-entity-preloader
+```
+
+## Usage
+
+Below is a basic example demonstrating how to use `EntityPreloader` to preload related entities and avoid the n+1 problem:
+
+```php
+use ShipMonk\DoctrineEntityPreloader\EntityPreloader;
+
+$categories = $entityManager->getRepository(Category::class)->findAll();
+
+$preloader = new EntityPreloader($entityManager);
+$articles = $preloader->preload($categories, 'articles'); // 1 query to preload articles
+$preloader->preload($articles, 'tags'); // 1 query to preload tags
+$preloader->preload($articles, 'comments'); // 1 query to preload comments
+
+// no more queries are needed now
+foreach ($categories as $category) {
+    foreach ($category->getArticles() as $article) {
+        echo $article->getTitle(), "\n";
+
+        foreach ($articles->getTags() as $tag) {
+            echo $tag->getLabel(), "\n";
+        }
+
+        foreach ($articles->getComments() as $comment) {
+            echo $comment->getText(), "\n";
+        }
+    }
+}
+```
+
+## Comparison vs. Fetch Joins
+
+Unlike fetch joins, the EntityPreloader does not fetches duplicate data, which slows down both the query and the hydration process, except when necessary to prevent additional queries fired by Doctrine during hydration process.
+
+## Comparison vs. `Doctrine\ORM\AbstractQuery::setFetchMode`
+
+Unlike `setFetchMode` it can
+
+* preload nested associations
+* preload `#[ManyToMany]` association
+* avoid additional queries fired by Doctrine during hydration process
+
+## Configuration
+
+`EntityPreloader` allows you to adjust batch sizes and fetch join limits to fit your application's performance needs:
+
+- **Batch Size:** Set a custom batch size for preloading to optimize memory usage.
+- **Max Fetch Join Same Field Count:** Define the maximum number of join fetches allowed per field.
+
+```php
+$preloader->preload(
+    $articles,
+    'category',
+    batchSize: 20,
+    maxFetchJoinSameFieldCount: 5
+);
+```
+
+
+## Limitations
+
+- no support for indexed collections
+- no support for dirty collections
+- no support for composite primary keys