Update README with detailed documentation and adjust project group ID

- Rewrote README with comprehensive documentation for surf-transaction, including features, core concepts, installation, and example usage.
- Updated `build.gradle.kts` to reflect a new group ID (`dev.slne.surf.transaction`) for better project organization.

Author: twisti-dev

README.md

@@ -1,3 +1,62 @@
-# SURF-TRANSACTION
+# surf-transaction
 
-Unfinished project port of the old transaction api.
+**surf-transaction** is a modular transaction system for the Surf ecosystem.
+It provides a structured API for managing accounts, currencies, and transactions and is designed for
+asynchronous use in plugins and modules.
+
+## Features
+
+* Account-based transaction system
+* Support for multiple currencies with configurable scaling
+* Deposits, withdrawals, and transfers
+* User- and account-centric API design
+* Extensible transaction metadata
+* Clear separation between public API and internal implementation
+
+## Installation
+
+### Gradle (Kotlin DSL)
+
+```kotlin
+dependencies {
+    implementation("dev.slne.surf.transaction:surf-transaction-api:<version>")
+}
+```
+
+## Core Concepts
+
+The API is built around a small set of core abstractions:
+
+* **TransactionUser**
+  Entry point for user-scoped transactions and account access.
+
+* **Account**
+  Accounts that hold balances in one or more currencies.
+
+* **Currency**
+  Defines currencies including symbol, scale, and minimum amount.
+
+* **Transaction**
+  Immutable representation of a completed transaction.
+
+## Example
+
+```kotlin
+val user = TransactionUser.byUuid(userUuid)
+
+user.deposit(
+    amount = BigDecimal("100"),
+    currency = Currency.default()
+)
+
+val balance = user.balance(Currency.default())
+```
+
+All transaction operations return a `TransactionResult`, which can be used to evaluate success or
+failure.
+
+## Internal APIs
+
+APIs annotated with `@InternalTransactionApi` are **not part of the public API** and must not be
+used.
+They may change or be removed at any time without notice.

build.gradle.kts

@@ -9,6 +9,6 @@ buildscript {
 }
 
 allprojects {
-    group = "dev.slne.surf"
+    group = "dev.slne.surf.transaction"
     version = findProperty("version") as String
 }