README refers to non-existant FlushPolicyBase class

[cookbr]

README.md references a FlushPolicyBase class ...

You can create a custom FlushPolicy special for your application needs by implementing the IFlushPolicy interface. You can also extend the FlushPolicyBase class that already creates and handles the shouldFlush value reset.

... but FlushPolicyBase doesn't exist.

[wenxi-zeng]

@cookbr thanks for reporting this. yeah, we don't have FlushPolicyBase in c#. the description was copied from our react-native library. we will get the docs fixed. in c#, just follow the example to implement IFlushPolicy