Added readme to CLR/regex sample

Author: JocaPC

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

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+# Implementing Regular Expressions in SQL Server using CLR UDF 
+SQL Database don't have built-in support for regular expressions, so the only workaround is to use Regular Expressions that exist in .Net framework and expose them as T-SQL functions.
+This code sample demonstrates how to create CLR User-Defined functions that expose regular expression functionalities that exist in .Net framework.
+
+### 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 2005+ Enterprise / Developer / Evaluation Edition
+2. **Key features:**
+    - CLR
+3. **Programming Language:** .NET C#
+4. **Author:** 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 Retail mode.
+3. Open and save SqlClrRegEx.tt to generate output T-SQL file that will contain script that inserts .dll file with the Regex functions, and exposes them as T-SQL/CLR functions.
+
+<a name=add-functions></a>
+## Add RegEx functions to your SQL database
+
+File SqlClrRegEx.sql contains the code that will import functions 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 regex functions. The script depends on the location where you have built the project, and might look like:
+```
+--Create the assembly
+CREATE ASSEMBLY SqlClrRegEx FROM 'D:\GitHub\sql-server-samples\samples\features\sql-clr\RegEx\bin\Release\SqlClrRegEx.dll' WITH PERMISSION_SET = SAFE
+GO
+
+CREATE SCHEMA REGEX;
+GO
+
+--Create the functions
+CREATE FUNCTION REGEX.MATCH (@src NVARCHAR(MAX), @regex NVARCHAR(4000))
+RETURNS BIT
+AS EXTERNAL NAME SqlClrRegEx.RegEx.CompiledMatch
+GO
+CREATE FUNCTION REGEX.SUBSTRING (@src NVARCHAR(MAX), @regex NVARCHAR(4000))
+RETURNS NVARCHAR(4000)
+AS EXTERNAL NAME SqlClrRegEx.RegEx.CompiledSubstring
+GO
+CREATE FUNCTION REGEX.REPLACE (@src NVARCHAR(MAX), @regex NVARCHAR(MAX), @value NVARCHAR(4000))
+RETURNS NVARCHAR(MAX)
+AS EXTERNAL NAME SqlClrRegEx.RegEx.CompiledReplace
+GO
+```
+
+This code will import assembly in SQL Database and add three functions that provide RegEx functionalities.
+
+<a name=test></a>
+
+## Test the functions
+
+Once you create the assembly and expose the functions, you can use regular expression functionalities in T-SQL code:
+
+```
+IF( REGEX.MATCH('tst123test', '[0-9]+') = 1 )
+	SELECT REGEX.SUBSTRING('tst123test', '[0-9]+'), REGEX.REPLACE('tst123test', '[0-9]+', 'XXX')
+```
+
+<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.
+