Update README to emphasize built-in filters are add automatically and adjust wording (#448)

* update README

* remove unused reference

Author: zhiyuanliang-ms

README.md

@@ -533,7 +533,7 @@ If all of three filters are registered:
 
 ## Built-In Feature Filters
 
-There a few feature filters that come with the `Microsoft.FeatureManagement` package: `PercentageFilter`, `TimeWindowFilter`, `ContextualTargetingFilter` and `TargetingFilter`. All filters, except for the `TargetingFilter`, are added automatically when feature management is registered. The `TargetingFilter` is added with the `WithTargeting` method that is detailed in the `Targeting` section below.
+There a few feature filters that come with the `Microsoft.FeatureManagement` package: `PercentageFilter`, `TimeWindowFilter`, `ContextualTargetingFilter` and `TargetingFilter`. All filters, except for the `TargetingFilter`, are added **automatically** when feature management is registered by `AddFeatureManagement` method. The `TargetingFilter` is added with the `WithTargeting` method that is detailed in the `Targeting` section below.
 
 Each of the built-in feature filters have their own parameters. Here is the list of feature filters along with examples.
 
@@ -603,7 +603,7 @@ The `Recurrence` settings is made up of two parts: `Pattern` (how often the time
 
 #### Recurrence Pattern
 
-There are two possible recurrence pattern types: `Daily` and `Weekly`. For example, a time window could repeat "every day", "every 3 days", "every Monday" or "on Friday per 2 weeks". 
+There are two possible recurrence pattern types: `Daily` and `Weekly`. For example, a time window could repeat "every day", "every 3 days", "every Monday" or "every other Friday". 
 
 Depending on the type, certain fields of the `Pattern` are required, optional, or ignored.
 

src/Microsoft.FeatureManagement/Targeting/ContextualTargetingFilter.cs

@@ -5,7 +5,6 @@
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using System;
-using System.Collections.Generic;
 using System.Linq;
 using System.Security.Cryptography;
 using System.Text;