Add readme for NuGet package documentation

NuGet README.md

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+# LINQPad.QueryPlanVisualizer 
+
+[![NuGet Version](https://buildstats.info/NuGet/LINQPadQueryPlanVisualizer)](https://www.NuGet.org/packages/LINQPadQueryPlanVisualizer/) [![Apache license](http://img.shields.io/badge/license-Apache-brightgreen.svg)](https://github.com/Giorgi/QueryPlanVisualizer/blob/master/LICENSE.md)
+
+## SQL Server and PostgreSQL query execution plan visualizer for LINQPad
+
+![Icon](IconSmall.png "icon")
+
+## Features
+
+* View query execution plan inside LINQPad
+* View missing indexes for query
+* Share plan to [https://www.brentozar.com/pastetheplan/](https://www.brentozar.com/pastetheplan/) or [https://explain.dalibo.com/](https://explain.dalibo.com/)
+* Create missing indexes directly from LINQPad
+* Open plan in SQL Server Management Studio or another default app
+* Save plan to disk
+
+## Getting Started
+
+**If you use LINQPad 6, you must use version 2.0 of this library. For LINQPad 5, you must use version 1.0**
+
+The library can show query plans for `LINQ to SQL` driver and `Entity Framework Core 5`.
+
+### Install from NuGet
+
+If you have a Developer or higher edition of LINQPad, you can use the `LINQPadQueryPlanVisualizer` package from NuGet
+to add the visualizer to your queries.
+
+### Install as plugin
+
+To install the visualizer as a LINQPad plugin, download the [latest release](https://github.com/Giorgi/QueryPlanVisualizer/releases/latest) and drop the visualizer dll directly inside LINQPad's plugins folder (by default found at **My Documents\LINQPad Plugins\NetCore3** for LINQPad 6 and **My Documents\LINQPad Plugins\Framework 4.6** for LINQPad 5). The plugin will be automatically available in all your queries.
+
+## Viewing query plan
+
+To view query plan or missing indexes, call static `QueryPlanVisualizer.DumpPlan(query)` method or call `DumpPlan` extension method on an `IQueryable` instance. You will also need to add `ExecutionPlanVisualizer` to the namespaces list (click F4 to open the dialog). If you want to dump query result as well, pass `true` as a second parameter.