Updated Readme files

pkg/writers/bun/README.md

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+# Bun Writer
+
+Generates Go source files with Bun model definitions from database schema information.
+
+## Overview
+
+The Bun Writer converts RelSpec's internal database model representation into Go source code with Bun struct definitions, complete with proper tags, relationships, and table configuration.
+
+## Features
+
+- Generates Bun-compatible Go structs
+- Creates proper `bun` struct tags
+- Adds relationship fields
+- Supports both single-file and multi-file output
+- Maps SQL types to Go types
+- Handles nullable fields with sql.Null* types
+- Generates table aliases
+
+## Usage
+
+### Basic Example
+
+```go
+package main
+
+import (
+    "git.warky.dev/wdevs/relspecgo/pkg/models"
+    "git.warky.dev/wdevs/relspecgo/pkg/writers"
+    "git.warky.dev/wdevs/relspecgo/pkg/writers/bun"
+)
+
+func main() {
+    options := &writers.WriterOptions{
+        OutputPath:  "models.go",
+        PackageName: "models",
+    }
+
+    writer := bun.NewWriter(options)
+    err := writer.WriteDatabase(db)
+    if err != nil {
+        panic(err)
+    }
+}
+```
+
+### CLI Examples
+
+```bash
+# Generate Bun models from PostgreSQL database
+relspec --input pgsql \
+  --conn "postgres://localhost/mydb" \
+  --output bun \
+  --out-file models.go \
+  --package models
+
+# Convert GORM models to Bun
+relspec --input gorm --in-file gorm_models.go --output bun --out-file bun_models.go
+
+# Multi-file output
+relspec --input json --in-file schema.json --output bun --out-file models/
+```
+
+## Generated Code Example
+
+```go
+package models
+
+import (
+    "time"
+    "database/sql"
+    "github.com/uptrace/bun"
+)
+
+type User struct {
+    bun.BaseModel `bun:"table:users,alias:u"`
+
+    ID        int64     `bun:"id,pk,autoincrement" json:"id"`
+    Username  string    `bun:"username,notnull,unique" json:"username"`
+    Email     string    `bun:"email,notnull" json:"email"`
+    Bio       sql.NullString `bun:"bio" json:"bio,omitempty"`
+    CreatedAt time.Time `bun:"created_at,notnull,default:now()" json:"created_at"`
+
+    // Relationships
+    Posts []*Post `bun:"rel:has-many,join:id=user_id" json:"posts,omitempty"`
+}
+
+type Post struct {
+    bun.BaseModel `bun:"table:posts,alias:p"`
+
+    ID      int64          `bun:"id,pk" json:"id"`
+    UserID  int64          `bun:"user_id,notnull" json:"user_id"`
+    Title   string         `bun:"title,notnull" json:"title"`
+    Content sql.NullString `bun:"content" json:"content,omitempty"`
+
+    // Belongs to
+    User *User `bun:"rel:belongs-to,join:user_id=id" json:"user,omitempty"`
+}
+```
+
+## Supported Bun Tags
+
+- `table` - Table name and alias
+- `column` - Column name (auto-derived if not specified)
+- `pk` - Primary key
+- `autoincrement` - Auto-increment
+- `notnull` - NOT NULL constraint
+- `unique` - Unique constraint
+- `default` - Default value
+- `rel` - Relationship definition
+- `type` - Explicit SQL type
+
+## Type Mapping
+
+| SQL Type | Go Type | Nullable Type |
+|----------|---------|---------------|
+| bigint | int64 | sql.NullInt64 |
+| integer | int | sql.NullInt32 |
+| varchar, text | string | sql.NullString |
+| boolean | bool | sql.NullBool |
+| timestamp | time.Time | sql.NullTime |
+| numeric | float64 | sql.NullFloat64 |
+
+## Notes
+
+- Model names are derived from table names (singularized, PascalCase)
+- Table aliases are auto-generated from table names
+- Multi-file mode: one file per table named `sql_{schema}_{table}.go`
+- Generated code is auto-formatted
+- JSON tags are automatically added