odroid_h4 overview.md: Add a short description

Signed-off-by: Filip Gołaś <[email protected]>

docs/variants/hardkernel_odroid_h4/overview.md

@@ -1,9 +1,26 @@
 # Overview
 
-- [Releases](./releases.md)
-- [Building Manual](./building-manual.md)
-- [Initial Deployment](./initial-deployment.md)
-- [Firmware Update](./firmware-update.md)
-- [Recovery](./recovery.md)
-- [Hardware Configuration Matrix](./hardware-matrix.md)
-- [Test Matrix](./test-matrix.md)
+## Hardkernel ODROID-H4 PLUS
+
+Hardkernel ODROID-H4 PLUS is a small open-source hardware single-board computer.
+One of it's most noteworthy features is the use of two distinct switchable BIOS
+flash memory chips which makes it a perfect device for experimenting with
+firmware by making the recovery process after bricking the device a breeze.
+
+## Documentation
+
+- [Releases](./releases.md) - Groups information about all releases.
+- [Building Manual](./building-manual.md) - Describes how to build Dasharo
+  compatible with the ODROID-H4 PLUS.
+- [Initial Deployment](./initial-deployment.md) - Describes initial Dasharo
+  deployment methods (i. e. flashing new firmware) compatible with ODROID-H4
+  PLUS.
+- [Firmware Update](./firmware-update.md) - Explains supported Dasharo
+    open-source firmware update methods.
+- [Recovery](./recovery.md) - Gathers information on how to recover the platform
+    from potential failure.
+- [Hardware Configuration Matrix](./hardware-matrix.md) - Describes the
+    platform's hardware configuration used during the Dasharo firmware
+    validation procedure.
+- [Test Matrix](./test-matrix.md) - Describes validation scope used during
+    Dasharo firmware validation procedure.