Add Gmail SMTP option + docs

docs/self-hosting/configuration/email.mdx

@@ -23,7 +23,7 @@ By default, you need to configure the following SMTP [environment variables](htt
 - `SMTP_FROM_ADDRESS`: Email address to be used for sending emails (e.g. [email protected]).
 - `SMTP_FROM_NAME`: Name label to be used in `From` field (e.g. Team).
 
-Below you will find details on how to configure common email providers (not in any particular order).
+Below you will find details on how to configure common email providers:
 
 <AccordionGroup>
 <Accordion title="Twilio SendGrid">
@@ -135,6 +135,34 @@ SMTP_FROM_NAME=Infisical
 </Info>
 </Accordion>
 
+<Accordion title="Gmail">
+
+Create an account and enable "less secure app access" in Gmail Account Settings > Security. This will allow
+applications like Infisical to authenticate with Gmail via your username and password.
+
+![Gmail secure app access](../../images/email-gmail-app-access.png)
+
+With your Gmail username and password, you can set your SMTP environment variables:
+
+```
+SMTP_HOST=smtp.gmail.com
+[email protected] # your email
+SMTP_PASSWORD=password # your password
+SMTP_PORT=587
+SMTP_SECURE=true
+[email protected]
+SMTP_FROM_NAME=Infisical
+```
+
+<Warning>
+  As per the [notice](https://support.google.com/accounts/answer/6010255?hl=en) by Google, you should note that using Gmail credentials for SMTP configuration
+  will only work for Google Workspace or Google Cloud Identity customers as of May 30, 2022.
+
+  Put differently, the SMTP configuration is only possible with business (not personal) Gmail credentials.
+</Warning>
+
+</Accordion>
+
 <Accordion title="Zoho Mail">
 
 1. Create an account and configure [Zoho Mail](https://www.zoho.com/mail/) to send emails.