Add new configuration document for connection sendgrid (#115)

docs/reference/config-files/connection/sendgrid.md

@@ -0,0 +1,38 @@
+---
+title: sendgrid
+sidebar_label: sendgrid
+---
+
+# sendgrid
+
+The `sendgrid` connection can be used to access SendGrid resources.
+
+```hcl
+connection "sendgrid" "my_sendgrid" {
+  api_key = "SG.R7..."
+}
+```
+
+## Arguments
+
+| Name      | Type   | Required? | Description      |
+| --------- | ------ | --------- | ---------------- |
+| `api_key` | String | Optional  | SendGrid API Key |
+
+All arguments are optional, and a `sendgrid` connection with no arguments will behave the same as the [default connection](#default-connection).
+
+## Attributes (Read-Only)
+
+| Attribute | Type | Description                                                                         |
+| --------- | ---- | ----------------------------------------------------------------------------------- |
+| `env`     | Map  | A map of the resolved connection-related environment variables (`SENDGRID_API_KEY`) |
+
+## Default Connection
+
+The `sendgrid` connection type includes an implicit, default connection (`connection.sendgrid.default`) that will be configured to set the `api_key` to the `SENDGRID_API_KEY` environment variable.
+
+```hcl
+connection "sendgrid" "default" {
+  api_key = env("SENDGRID_API_KEY")
+}
+```