Fix formatting and wording in extension-supported OS doc

Author: przlplx

support/azure/virtual-machines/windows/extension-supported-os.md

@@ -6,7 +6,7 @@ ms.reviewer:
 ms.service: azure-virtual-machines
 ms.custom: sap:VM Extensions not operating correctly
 ---
-# Azure extensions-supported operating systems
+# Azure extension-supported operating systems
 
 **Applies to:** :heavy_check_mark: Linux VMs :heavy_check_mark: Windows VMs
 
@@ -18,9 +18,9 @@ _Original KB number:_   4078134
 VM extensions enable post-deployment configuration of a virtual machine (VM), including installing and configuring software. VM extensions also enable recovery features, such as resetting the administrative password of a VM. Without the Azure VM Agent, VM extensions can't be run.
 
 * In order to run, the Windows VM Agent requires at least Windows Server 2008 SP2 (64-bit) and .NET Framework 4.0.
-* The Linux agent runs on [multiple OSes](/azure/virtual-machines/extensions/agent-linux#requirements). However, the extensions framework has a limit for the OSes that support extensions.
+* The Linux agent runs on [multiple systems](/azure/virtual-machines/extensions/agent-linux#requirements). However, the extensions framework has a limit for the systems that support extensions.
 
-Some extensions are not supported across all OSes. They might return Error Code 51, 'Unsupported OS'. Check the individual extension documentation for supportability.
+Some extensions aren't supported across all systems. They might return Error Code 51, 'Unsupported OS'. Check the individual extension documentation for supportability.
 
 For a discussion about Windows and Linux extensions and how to troubleshoot extensions, see [Azure virtual machine extensions and features](/azure/virtual-machines/extensions/overview).