Added README to TCC sample

Author: JocaPC

samples/features/sql-clr/TransitiveClosure/README.md

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+# Implementing Transitive Closure Clustering in SQL Server using CLR UDF 
+SQL Database don't have built-in support for transitive closure clustering, so the only workaround is to implement this algorithm in .Net framework and expose it as T-SQL function.
+This code sample demonstrates how to create CLR User-Defined aggregate that implements clustering.
+
+### Contents
+
+[About this sample](#about-this-sample)<br/>
+[Build the CLR/RegEx functions](#build-functions)<br/>
+[Add RegEx functions to your SQL database](#add-functions)<br/>
+[Test the functions](#test)<br/>
+[Disclaimers](#disclaimers)<br/>
+
+<a name=about-this-sample></a>
+
+## About this sample 
+1. **Applies to:** SQL Server 2016+ Enterprise / Developer / Evaluation Edition
+2. **Key features:**
+    - CLR, JSON
+3. **Programming Language:** .NET C#
+4. **Author:** Davide Mauri, Jovan Popovic [jovanpop-msft]
+
+<a name=build-functions></a>
+
+## Build the CLR/RegEx functions
+
+1. Download the source code and open the solution using Visual Studio.
+2. Change the password in .pfk file and rebuild the solution in **Release** mode.
+3. Open and save TransitiveClosure.tt to generate output T-SQL file that will contain script that inserts .dll file with the Transitive closure clustering aggregate.
+
+<a name=add-functions></a>
+## Add Clustering aggregate to your SQL database
+
+File TransitiveClosure.sql contains the code that will import aggregate into SQL Database.
+
+If you have not added CLR assemblies in your database, you should use the following script to enable CLR:
+```
+sp_configure @configname=clr_enabled, @configvalue=1
+GO
+RECONFIGURE
+GO
+```
+
+Once you enable CLR, you can use the T-SQL script to add the clustering aggregate. The script depends on the location where you have built the project, and might look like:
+```
+CREATE ASSEMBLY TransitiveClosure FROM 'D:\GitHub\sql-server-samples\samples\features\sql-clr\TransitiveClosure\bin\Release\TransitiveClosureAggregatorLibrary.dll' WITH PERMISSION_SET = SAFE;
+GO
+
+CREATE SCHEMA TC;
+GO
+
+CREATE AGGREGATE TC.CLUSTERING(@id1 INT, @id2 INT)  
+RETURNS NVARCHAR(MAX)  
+EXTERNAL NAME TransitiveClosure.[TransitiveClosure.Aggregate]; 
+```
+
+This code will import assembly in SQL Database and add three functions that provide clustering functionalities.
+
+<a name=test></a>
+
+## Test the function
+
+Once you create the assembly and expose the functions, you can use it to cluster some relational data in T-SQL code:
+
+```
+declare @edges table(n1 int, n2 int);
+
+insert into @edges
+values (1,2),(2,3),(3,4),(4,5),(2,21),(2,22),
+              (7,8),(8,9),(9,10);
+
+select TC.CLUSTERING(n1,n2)
+from @edges;
+```
+
+<a name=disclaimers></a>
+
+## Disclaimers
+The code included in this sample is not intended to be a set of best practices on how to build scalable enterprise grade applications. This is beyond the scope of this sample.
+