Add the "project" option to support many projects

.gitignore

@@ -1 +1,3 @@
 .env
+.env.*
+!.env.dist

README.md

@@ -8,6 +8,8 @@ The import file supported is an export file from a [Toggl](https://toggl.com) ap
 
 ## Setup
 
+### Basic setup for a single project
+
 1. Create the `.env` file:
 ```bash
 cp .env.dist .env
@@ -26,6 +28,25 @@ Env variables prefixed with `TOGGL_` are optional if you use an `--import` optio
 * `TOGGL_CLIENT_ID`: The client ID in Toggl from whom you want to export your work logs.
 * `TOGGL_WORKSPACE_ID`: Your workspace ID in Toggl from whom you want to export your work logs.
 
+### Advanced setup for many project
+
+A very common case is that you want to import your worklogs into different Jira accounts from different Toggle accounts
+depending on the project. You can handle it with the `--project` option! We will consider two cases.
+
+#### CASE 1: One Toggl account and many Jira accounts
+
+In this case, you most likely work on many Jira projects and want to import all from your one Toggl account where you
+log everything. Let's say you work on two projects `sylius` and `symfony`. In your `.env` define common env variables so
+all prefixed with `TOGGL_`. In `.env.sylius` and `.env.symfony` specify env variables specific for your Jira account so
+prefixed with `ATLASSIAN_`. Now, if you run the command with `--project="symfony"`, files `.env` and `.env.symfony` will
+be used.
+
+#### CASE 2: A different Toggl account and Jira account for each project
+
+Similar to the case above but you leave `.env` empty. Instead of that file, you define all env vars right in
+`.env.<your-project-name>`.
+
+
 ## Usage
 
 Import from Toggl:

main.go

@@ -13,24 +13,34 @@ import (
 )
 
 func main() {
+	var project string
 	var records [][]string
 	var csvFilePathToImport string
 	var since string
 	var until string
 	var dryRun bool
 
-	err := godotenv.Load()
-	if err != nil {
-		fmt.Println("Error loading .env file.")
-		return
-	}
-
+	flag.StringVar(&project, "project", "", "A project name that will load .env.<project-name> file.")
 	flag.StringVar(&csvFilePathToImport, "import", "", "CSV file path to import.")
 	flag.StringVar(&since, "since", "", "Import work logs since date. Format YYYY-MM-DD.")
 	flag.StringVar(&until, "until", "", "Import work logs until date. Format YYYY-MM-DD.")
 	flag.BoolVar(&dryRun, "dry-run", false, "Dry run. Export work logs but do not import.")
 	flag.Parse()
 
+	err := godotenv.Load(".env")
+	if err != nil {
+		fmt.Println("Error loading .env file.")
+		return
+	}
+	if project != "" {
+		projectEnv := fmt.Sprintf(".env.%s", project)
+		err = godotenv.Load(projectEnv)
+		if err != nil {
+			fmt.Printf("Error loading %s file.\n", projectEnv)
+			return
+		}
+	}
+
 	optionsValidationFailed := false
 
 	if since == "" {