Add subghz readme files

subghz/README.md

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+# Sub-GHz
+The Flipper Zero "Sub-GHz" radio is used for receiving and transmitting frequencies below the 1GHz (1000MHz) range.  In particular, the firmware supports 300-348 MHz, 387-464 MHz, and 779-928 MHz operational bands.  Depending on your region there may be additional [restrictions](https://docs.flipperzero.one/sub-ghz/frequencies).
+
+This enlistment contains the following:
+- [Plugins](./plugins/README.md) are applications & games that can be added to the Flipper Zero.  These applications utilize the subghz radio.
+- [Protcols](./protocols/README.md) extend the Sub-GHz "Read" feature of your Flipper with the ability to support new protocols.
+- [Samples](./samples/README.md) are samples captured by various remotes I own.

subghz/plugins/README.md

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+# Sub-GHz Plugins
+Add new applications to your Flipper Zero that utilize the Sub-GHz protocol.
+
+- [Subghz demo](./subghz_demo/README.md) is a tutorial to demonstrate how to add Sub-GHz support into your own applications.
+- [Rock Paper Scissors](./rock_paper_scissors/README.md) is a two-player game that utilizes the Sub-GHz chat protocol.

subghz/protocols/README.md

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+# Sub-GHz Protocols
+Extend the Sub-GHz "Read" feature of your Flipper with the ability to support new protocols.
+
+- [X10](./x10/README.md) support for x10.com devices.

subghz/samples/README.md

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+# Sub-GHz Samples
+These are samples captured by various remotes I own.
+- [Chevy HHR 2006](./chevy-hhr-2006/README.md) vehicle keyfob.
+- [Quantum Fire](./quantum-fire/README.md) fireworks controller.
+- [X10](./x10/README.md) x10.com controller.
+
+Check out my [YouTube videos](../../youtube/README.md#sub-ghz) for more information on how to use these files.
+
+The file format is [documented](https://flipperdevices.github.io/flipperzero-firmware/md_docs_file_formats__sub_ghz_file_formats.html) on the flipperdevices github account.