Add .env_sample file

Author: thiagobbt

Diff for: .env_sample

@@ -0,0 +1 @@
+export SENDGRID_API_KEY=''

Diff for: .gitignore

@@ -12,4 +12,5 @@ target
 examples/Example.java
 .settings
 .classpath
-.project
+.project
+.env

Diff for: README.md

@@ -44,11 +44,13 @@ We appreciate your continued support, thank you!
 
 Update the development environment with your [SENDGRID_API_KEY](https://app.sendgrid.com/settings/api_keys), for example:
 
+1. Copy the sample environment file to a new file
 ```bash
-echo "export SENDGRID_API_KEY='YOUR_API_KEY'" > sendgrid.env
-echo "sendgrid.env" >> .gitignore
-source ./sendgrid.env
+cp .env_sample .env
 ```
+2. Edit the new `.env` to add your API key
+3. Source the `.env` file to set rhe variable in the current session
+
 ## Install Package
 
 Choose your installation method - Maven w/ Gradle (recommended), Maven or Jar file.