Add mailhog and ngrok descriptions

docs/developer/running-saleor/debugging-emails.mdx

@@ -0,0 +1,29 @@
+---
+title: Debugging emails
+sidebar_label: Debugging emails
+---
+
+[Saleor platform](https://github.com/mirumee/saleor-platform) uses [Mailhog](https://github.com/mailhog/MailHog) for catching all the emails sent by the Saleor. 
+
+![Mailhog user interface](../screenshots/mailhog.png)
+
+Pros of using Mailhog during development:
+- live preview of rendered emails.
+- no need to send emails to external services.
+- test emails will be caught in the local environment, so there is no possibility of sending test data to actual customers.
+- eliminates possibility of sending emails to non existing address, which can hurt email reputation.
+
+## Configuration
+
+### Saleor Platform
+
+There is no need for additional configuration. Everything works out of the box.
+
+### Local development environment
+
+1. Follow [the installation guide](https://github.com/mailhog/MailHog#installation).
+2. Set Mailhog SMTP server address (`smtp://localhost:1025`) at plugins configuration page for [AdminEmails](developer/available-plugins/admin-emails.mdx) and [UserEmails](developer/available-plugins/user-emails.mdx) 
+
+## Access to the interface
+
+Visit [http://localhost:8025](http://localhost:8025).

docs/developer/running-saleor/exposing-instance.mdx

@@ -0,0 +1,21 @@
+---
+title: Exposing local instance
+sidebar_label: Exposing instance
+---
+
+There are situations when you would like to expose your local environment to external clients, for example:
+
+- show your project to the manager.
+- integrate with the new payment gateway, which requires a return URL.
+- testing app deployed in the cloud.
+
+To achieve that, you need a service for redirecting the traffic. Such service is delivered by [ngrok](https://ngrok.com) and [localtunnel](https://localtunnel.me). Both are great for our use case, and you can choose any of those services.
+
+## Using ngrok
+
+1. Append ngrok URL to `ALLOWED_CLIENT_HOSTS` environment varible
+2. Start Saleor on your machine
+3. Follow [ngrok installation guide](https://ngrok.com/product)
+4. Start a tunnel in your command line `ngrok http 8000`
+5. Your server is now exposed under ngrok domain (for example: http://92832de0.ngrok.io). Copy that address.
+6. Enter ngrok URL at [Site Settings](dashboard/configuration/site.md) configuration.

website/sidebars.js

@@ -143,6 +143,8 @@ module.exports = {
           "developer/running-saleor/s3",
           "developer/running-saleor/gcs",
           "developer/running-saleor/emails",
+          "developer/running-saleor/debugging-emails",
+          "developer/running-saleor/exposing-instance",
           "developer/running-saleor/monitoring",
           "developer/running-saleor/background-tasks"
         ]