Add documentation page for version

The version command, although not the mightiest of our commands,
did not have a page among our docs.

website/docs/commands/version.html.markdown

@@ -0,0 +1,55 @@
+---
+layout: "docs"
+page_title: "Command: version"
+sidebar_current: "docs-commands-version"
+description: |-
+  The `terraform version` command displays the version of Terraform and all installed plugins.
+---
+
+# Command: version
+
+The `terraform version` displays the current version of Terraform and all
+installed plugins.
+
+## Usage
+
+Usage: `terraform version [options]`
+
+With no additional arguments, `version` will display the version of Terraform,
+the platform it's installed on, installed providers, and the results of upgrade
+and security checks [unless disabled](/docs/commands/index.html#upgrade-and-security-bulletin-checks).
+
+This command has one optional flag:
+
+* `-json` - If specified, the version information is formatted as a JSON object, 
+    and no upgrade or security information is included.
+
+-> **Note:** Platform information was added to the `version` command in Terraform 0.15. 
+
+## Example
+
+Basic usage, with upgrade and security information shown if relevant:
+
+```shellsession
+$ terraform version
+Terraform v0.15.0
+on darwin_amd64
++ provider registry.terraform.io/hashicorp/null v3.0.0
+
+Your version of Terraform is out of date! The latest version
+is X.Y.Z. You can update by downloading from https://www.terraform.io/downloads.html
+```
+
+As JSON:
+
+```shellsession
+$ terraform version -json
+{
+  "terraform_version": "0.15.0",
+  "platform": "darwin_amd64",
+  "provider_selections": {
+    "registry.terraform.io/hashicorp/null": "3.0.0"
+  },
+  "terraform_outdated": true
+}
+```