Split platforms in supported "tiers"

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Author: troglobit

_tabs/platforms.md

@@ -3,24 +3,54 @@ icon: fas fa-microchip
 order: 3
 ---
 
-Infix can run on many different types of architectures and boards, much
-thanks to Linux and Buildroot.  Currently the focus is on 64-bit ARM
-devices with switching fabric supported by Linux switchdev.
+Infix can run on many different types of [architectures and boards][1],
+much thanks to Linux and Buildroot.  Currently the focus is on 64-bit
+ARM devices with switching fabric supported by Linux switchdev.
 
-The [following boards][1] are fully supported:
+The following boards have been know to run Infix.  They are divided into
+three tiers to denote level of support.
 
- - Marvell CN9130 CRB (ARM)
- - Marvell EspressoBIN (ARM)
- - Microchip SparX-5i PCB135 (ARM)
- - StarFive VisionFive2 (RISC-V)
- - NanoPi R2S (ARM)
+### Tier 1
 
-An x86_64 build is also available, primarily intended for development
-and testing using [Qemu][2], but can also be used for evaluation and
-demo purposes in [GNS3][3].  For more information, see: [Infix in
-Virtual Environments][4].
+Fully supported in default builds, with images included in releases:
+
+ - [Marvell CN9130][5] CRB (ARM)
+ - Qemu[^1] (x86_64)
+
+### Tier 2
+
+Separate `defconfig`, may use custom kernel and bootloader.  May
+graduate to *Tier 1* support depending on community interest and
+participation.
+
+ - [StarFive VisionFive2][6] (RISC-V)
+ - [NanoPi R2S][7] (ARM)
+
+### Tier 3
+
+Worked at one point but needs more attention to bring on par with the
+Infix boot sequence, and testing:
+
+ - [Microchip SparX-5i][8] PCB135 (ARM)
+ - [Marvell EspressoBIN][9] (ARM)
+
+
+
+------
+
+**Footnotes**
+
+[^1]: The [Qemu][2] x86_64 is primarily intended for development and
+    testing, but can also be used for evaluation and demo purposes in
+    [GNS3][3].  For more information, see: [Infix in Virtual
+    Environments][4].
 
 [1]: https://github.com/kernelkit/infix/tree/main/board
 [2]: https://www.qemu.org/
 [3]: https://www.gns3.com/
 [4]: https://github.com/kernelkit/infix/blob/main/doc/virtual.md
+[5]: https://www.marvell.com/content/dam/marvell/en/public-collateral/embedded-processors/marvell-infrastructure-processors-octeon-tx2-cn913x-product-brief.pdf
+[6]: https://doc-en.rvspace.org/VisionFive2/Landing_Page/VisionFive_2/introduction.html
+[7]: https://wiki.friendlyelec.com/wiki/index.php/NanoPi_R2S
+[8]: https://ww1.microchip.com/downloads/en/DeviceDoc/00002854B.pdf
+[9]: http://espressobin.net/