o update readmes.

adapter/passive-3/README.md

@@ -1,15 +1,16 @@
 Adapter PCB to support up to 3 panels
 ======================================
 
+   * Passive board. Simple, but might need to define `RGB_SLOWDOWN_GPIO` if you see
+     glitches. Consider using the [active board](../active-3) in that case.
    * Supports up to three panel chains for newer plus models and
      Raspberry Pi 2 that have 40 GPIO pins.
    * Open source KiCAD PCB EDA format.
    * (not very pretty layout, was just lazy and let the auto-router do it).
-     
+
 You can [buy the board from OSH Park][osh-passive3].
 
 ![Preview][rendering]
 
 [rendering]: ../../img/passive3-pcb.png
 [osh-passive3]: https://oshpark.com/shared_projects/FNAtZUsP
-

adapter/passive-rpi1/README.md

@@ -0,0 +1,16 @@
+Adapter PCB to connect to Rasbperry Pi1
+=======================================
+
+   * Passive board. Simple, but might need to define `RGB_SLOWDOWN_GPIO` if you see
+     glitches.
+   * Supports one panel connected to a 26 pin Raspberry Pi 1. If you have a newer RPi,
+     check out the [Passive 3](../passive3) or [Active 3](../active-3) adapter.
+   * Open source KiCAD PCB EDA format.
+   * (not very pretty layout, was just lazy and let the auto-router do it).
+
+You can [buy the board from OSH Park][osh-passive-rpi].
+
+![Preview][rendering]
+
+[rendering]: ../../img/passive-rpi1-pcb.png
+[osh-passive-rpi]: https://oshpark.com/shared_projects/afEA1gNt