CSHARP-2763: Create reference documentation for compression.

Author: DmitryLukyanov

Docs/reference/content/reference/driver/crud/compression.md

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+date = "2020-01-29T22:05:03-04:00"
+title = "Compression"
+[menu.main]
+  parent = "Reference Reading and Writing"
+  identifier = "Compression"
+  weight = 25
+  pre = "<i class='fa'></i>"
++++
+
+## Compression
+
+The C# driver supports compression of messages to and from MongoDB servers. The driver implements the three algorithms that are supported by MongoDB servers:
+
+* [Snappy](https://google.github.io/snappy/): Snappy compression can be used when connecting to MongoDB servers starting with the 3.4 release.
+* [Zlib](https://zlib.net/): Zlib compression can be used when connecting to MongoDB servers starting with the 3.6 release.
+* [Zstandard](https://facebook.github.io/zstd/): Zstandard compression can be used when connecting to MongoDB servers starting with the 4.2 release.
+
+The driver will negotiate which, if any, compression algorithm is used based on capabilities advertised by the server in the [ismaster]({{<docsref "reference/command/isMaster/">}}) command response. 
+
+### Specify compression via `Connection String`
+
+```c#
+using MongoDB.Driver;
+```
+
+To specify compression with [`ConnectionString`]({{<apiref "T_MongoDB_Driver_Core_Configuration_ConnectionString">}}), just add `compressors` into the connection string, as in:
+
+```c#
+var connectionString = "mongodb://localhost/?compressors=snappy";
+var client = new MongoClient(connectionString);
+```
+for Snappy compression, or
+
+```c#
+var connectionString = "mongodb://localhost/?compressors=zlib";
+var client = new MongoClient(connectionString);
+```
+for zlib compression, or 
+
+```c#
+var connectionString = "mongodb://localhost/?compressors=zstd";
+var client = new MongoClient(connectionString);
+```
+for Zstandard compression, or 
+
+```c#
+var connectionString = "mongodb://localhost/?compressors=snappy,zlib,zstd";
+var client = new MongoClient(connectionString);
+```
+to configure multiple compressors.
+
+In all cases the driver will use the first compressor in the list for which the server advertises support. 
+
+Additionally, zlib compression allows specifying a compression level with supported values between -1 and 9:
+
+```c#
+var connectionString = "mongodb://localhost/?compressors=zlib;zlibcompressionlevel=6";
+var client = new MongoClient(connectionString);
+```
+
+### Specify compression via `MongoClientSettings`
+
+```c#
+using MongoDB.Driver;
+using MongoDB.Driver.Core.Compression;
+using MongoDB.Driver.Core.Configuration;
+using System.Collections.Generic;
+```
+
+To specify compression with [`MongoClientSettings`]({{<apiref "T_MongoDB_Driver_MongoClientSettings">}}), set the `Compressors` property to a list of [`CompressorConfiguration`]({{<apiref "T_MongoDB_Driver_Core_Configuration_CompressorConfiguration">}}) instances:
+
+```c#
+var mongoClientSettings = new MongoClientSettings();
+mongoClientSettings.Compressors = new List<CompressorConfiguration>()
+{
+	new CompressorConfiguration(CompressorType.Snappy)
+};
+var client = new MongoClient(mongoClientSettings);
+```
+for Snappy compression, or
+
+```c#
+var mongoClientSettings = new MongoClientSettings();
+mongoClientSettings.Compressors = new List<CompressorConfiguration>()
+{
+	new CompressorConfiguration(CompressorType.Zlib)
+};
+var client = new MongoClient(mongoClientSettings);
+```
+for zlib compression, or
+
+```c#
+var mongoClientSettings = new MongoClientSettings();
+mongoClientSettings.Compressors = new List<CompressorConfiguration>()
+{
+	new CompressorConfiguration(CompressorType.Zstd)
+};
+var client = new MongoClient(mongoClientSettings);
+```
+for Zstandard compression, or
+
+```c#
+var mongoClientSettings = new MongoClientSettings();
+mongoClientSettings.Compressors = new List<CompressorConfiguration>()
+{
+	new CompressorConfiguration(CompressorType.Snappy),
+	new CompressorConfiguration(CompressorType.Zlib),
+	new CompressorConfiguration(CompressorType.Zstd)
+};
+var client = new MongoClient(mongoClientSettings);
+```
+to configure multiple compressors. 
+
+As with configuration via connection string, the driver will use the first compressor in the list for which the server advertises support. Also, the driver allows specifying a compression level option for zlib compression:
+
+```c#
+	var mongoClientSettings = new MongoClientSettings();
+	var compressorConfiguration = new CompressorConfiguration(CompressorType.Zlib);
+	compressorConfiguration.Properties.Add("Level", 6);
+	mongoClientSettings.Compressors = new List<CompressorConfiguration>() { compressorConfiguration };
+	var client = new MongoClient(mongoClientSettings);
+```