Add note for differences on unix (#3268)

* Note the differences for Unix GetTempPath

The current documentation leads people who are developing on windows and deploying on unix down the wrong path.

* Referencing mono is unnecessary information.

* edits

Co-authored-by: Maira Wenzel <[email protected]>

Author: sclarson

xml/System.IO/Path.xml

@@ -1778,17 +1778,23 @@ Paths are resolved by calling the <xref:System.IO.Path.GetFullPath%2A> method be
   
 ## Remarks  
  This method checks for the existence of environment variables in the following order and uses the first path found:  
-  
-1.  The path specified by the TMP environment variable.  
+
+# [Windows](#tab/windows)
+
+1.  The path specified by the TMP environment variable.   
   
 2.  The path specified by the TEMP environment variable.  
   
 3.  The path specified by the USERPROFILE environment variable.  
   
 4.  The Windows directory.  
-  
-   
-  
+
+# [Linux](#tab/linux)
+
+1. The path specified by the TMPDIR environment variable.  
+
+---
+
 ## Examples  
  The following code shows how to call the <xref:System.IO.Path.GetTempPath%2A> method.