Create AlternativeRules.md SX documentation

Author: felickz

documentation/AlternativeRules.md

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+### Alternative Rules (SX0000-)
+Rules which are non-standard extensions to the default StyleCop behavior, and represent an alternative style which is adopted by some projects. Alternative rules are known to directly conflict with standard StyleCop rules.
+
+Identifier | Name | Description
+-----------|------|------------
+[SX1101](SX1101.md) | DoNotPrefixLocalMembersWithThis | A call to an instance member of the local class or a base class is prefixed with 'this.', within a C# code file. 
+[SX1309](SX1309.md) | FieldNamesMustBeginWithUnderscore | A field name does not begin with an underscore.
+[SX1309S](SX1309S.md) | StaticFieldNamesMustBeginWithUnderscore | A static field name does not begin with an underscore.