Add software requirements section (#84)

Author: ryanuber

website/docs/cloud-docs/agents/requirements.mdx

@@ -30,6 +30,31 @@ Use the following specifications as a reference:
  - This provides the agent with enough memory to complete run operations, such as `terraform plan`, `git clone`, and `sentinel apply`. This also supports operations such as uploading and downloading artifacts, constructing temporary execution environments, and parsing configurations.
  - If you enable request forwarding, we recommend that you add at least 250MB of additional memory. The agent may hold multiple forwarded requests and responses in memory until they are successfully executed and relayed to HCP Terraform. 
 
+## Software Requirements
+
+Agents may depend on third-party tooling for certain features and functionality.
+The tfc-agent itself does not have any direct dependency on any of the following
+tools, though most common uses of Terraform will require them. The agent makes
+the assumption that the following utilities are pre-installed, and their
+respective CLI commands available on the `$PATH` of the user running tfc-agent.
+
+* `git` - The Git CLI. May be used by the Terraform CLI when downloading modules
+ from remote Git servers. Git version 2.3 or greater is required.
+* `ssh` - The SSH CLI. Used by `git` when the remote source uses the SSH
+ protocol.
+
+In addition to the above tools, it is often useful to install the following
+optional software to support a broad range of uses. These tools may be used by
+Terraform's `local-exec` provisioners, an `external` data source, or a tfc-agent
+[hook script](/terraform/cloud-docs/agents/hooks).
+
+* `curl` - Simple command-line HTTP client.
+* `wget` - Simple command-line HTTP client.
+* `jq` - JSON data inspection utility.
+* `unzip` - Unarchiver for zip archives.
+* `tar` - Unarchiver for tar archives.
+* `gzip` - Decompression utility for gzipped archives.
+
 ## Networking Requirements
 
 In order for an agent to function properly, it must be able to make outbound TCP connections to the HCP Terraform application APIs. These requests may require perimeter networking as well as container host networking changes, depending on your environment. Refer to the [HCP Terraform IP Ranges documentation](/terraform/cloud-docs/architectural-details/ip-ranges) for more details on the IP ranges.