Merge pull request microsoft#126 from Microsoft/pmasl-patch-7

Create README.md

Author: pmasl

samples/demos/mssqltiger/Plan-Comparison/Offline/README.md

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+Simply open SSMS, open a query execution plan file (.sqlplan) using File -> Open File, or drag a plan file to SSMS window. 
+Once the file opens, right-click anywhere inside the tab (not necessarily on top of an operator) and select “Compare Showplan” to get the other .sqlplan file to compare. 
+This works with any .sqlplan files you have, even from older versions of SQL Server. 
+Also, this is an offline compare, so there’s no need to be connected to a SQL Server instance.
+
+More information on the Plan Comparison Tool can beb found at https://blogs.msdn.microsoft.com/sql_server_team/tag/comparison-tool