Update agent install instructions to say where the variable is

Author: keithduncan

docs/updating-agent.md

@@ -3,17 +3,15 @@
 ## Linux
 
 Packer installs the `buildkite-agent` using the [`packer/linux/scripts/install-buildkite-agent.sh`](packer/linux/scripts/install-buildkite-agent.sh)
-script.
+script. Update the `AGENT_VERSION` variable in this file to
+change which version is installed.
 
 The agent binary is downloaded from download.buildkite.com.
 
-Update the `AGENT_VERSION` variable to change which version is installed.
-
 ## Windows
 
 Packer installs the `buildkite-agent` using the [`packer/windows/scripts/install-buildkite-agent.ps1`](packer/windows/scripts/install-buildkite-agent.ps1)
-script.
+script. Update the `AGENT_VERSION` variable in this file to
+change which version is installed.
 
 The agent binary is downloaded from download.buildkite.com.
-
-Update the `AGENT_VERSION` variable to change which version is installed.