Add readmes for System.IO.Compression* (#78645)

* Add readmes for System.IO.Compression*

* Clarify NuGet package should not be used on ns2.0+

diff --git a/src/libraries/System.IO.Compression.Brotli/README.md b/src/libraries/System.IO.Compression.Brotli/README.md
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+# System.IO.Compression.Brotli
+Contains the source and tests of assembly System.IO.Compression.Brotli, which includes types used to compress and decompress stream and streamless data using the Brotli algorithm.
+
+## Contribution Bar
+- [x] [We consider new features, new APIs and performance changes](../../libraries/README.md#primary-bar)
+- [x] [We consider PRs that target this library for new source code analyzers](../../libraries/README.md#secondary-bars)
+
+See the [Help Wanted](https://github.com/dotnet/runtime/issues?q=is%3Aopen+is%3Aissue+label%3Aarea-System.IO.Compression+label%3A%22help+wanted%22) issues. We don't have a specific label for Brotli issues so you will need to read through the list and see if something is available.
+
+## Deployment
+`System.IO.Compression.Brotli` is included in the shared framework since .NET Core 2.1 and .NET standard 2.1.
+
+## See also
+ - [`System.IO.Compression`](../System.IO.Compression#readme)

diff --git a/src/libraries/System.IO.Compression.ZipFile/README.md b/src/libraries/System.IO.Compression.ZipFile/README.md
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+# System.IO.Compression.ZipFile
+Contains convenience methods for extracting and creating zip archives and zip entries to and from file system entries.
+
+Documentation can be found at https://learn.microsoft.com/dotnet/api/system.io.compression.zipfile and https://learn.microsoft.com/dotnet/api/system.io.compression.zipfileextensions.
+
+## Contribution Bar
+- [x] [We consider new features, new APIs and performance changes](../../libraries/README.md#primary-bar)
+- [x] [We consider PRs that target this library for new source code analyzers](../../libraries/README.md#secondary-bars)
+
+See the [Help Wanted](https://github.com/dotnet/runtime/issues?q=is%3Aopen+is%3Aissue+label%3Aarea-System.IO.Compression+label%3A%22help+wanted%22) issues. We don't have a specific label for ZipFile issues so you will need to read through the list and see if something is available.
+
+## Deployment
+`System.IO.Compression.ZipFile` is included in the shared framework. The package does not need to be installed into any project compatible with .NET Standard 2.0.
+
+## See also
+ - [`System.IO.Compression`](../System.IO.Compression#readme)

diff --git a/src/libraries/System.IO.Compression/README.md b/src/libraries/System.IO.Compression/README.md
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+# System.IO.Compression
+Contains the source and tests of assembly System.IO.Compression, that includes types widely used on the compression space, as well as types for zip manipulation, and implementations of the Deflate and Gzip algorithms.
+
+Documentation can be found at https://learn.microsoft.com/dotnet/api/system.io.compression.
+
+## System.IO.Compression.Native source
+[../../native/libs/System.IO.Compression.Native](../../native/libs/System.IO.Compression.Native) contains the PAL (Platform Abstraction Layer) of the zlib library used by System.IO.Compression.
+
+## Contribution Bar
+- [x] [We consider new features, new APIs and performance changes](../../libraries/README.md#primary-bar)
+- [x] [We consider PRs that target this library for new source code analyzers](../../libraries/README.md#secondary-bars)
+
+See the [Help Wanted](https://github.com/dotnet/runtime/issues?q=is%3Aopen+is%3Aissue+label%3Aarea-System.IO.Compression+label%3A%22help+wanted%22) issues.
+
+## Deployment
+`System.IO.Compression` is included in the shared framework. The package does not need to be installed into any project compatible with .NET Standard 2.0.
+
+## See also
+ - [`System.IO.Compression.Brotli`](../System.IO.Compression.Brotli#readme)
+ - [`System.IO.Compression.ZipFile`](../System.IO.Compression.ZipFile#readme)
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