pinephone-pro: add docs around kernel building

hosts/modules/hal/pine64-pinephone-pro/default.nix

@@ -1,6 +1,14 @@
 { config, lib, pkgs, ... }:
 let
   cfg = config.sane.hal.pine64-pinephone-pro;
+  # to perform iterative kernel development w/o full rebuilds every time:
+  # 1. use `nix-shell` to enter the environment for a kernel build.
+  # 2. `export out=$pwd/out`
+  # 3. `export dev=$pwd/dev`
+  # 4. `eval "$configurePhase"`
+  # 5. `eval "$buildPhase" && eval "$installPhase"`
+  # 6. `./scripts/deploy ...` to deploy the built kernel
+  # 7. repeat steps 5/6, tweaking the kernel src in between
   myCustomKernel = pkgs.linux-sane-pinephonepro.overrideAttrs (prev: {
     dontUnpack = true;
     dontPatch = true;
@@ -180,6 +188,10 @@ in
     #   );
     # });
 
+    # boot.blacklistedKernelModules = [
+    #   "rt5640"  #< doesn't seem to actually prevent rt5640 from being loaded?..
+    # ];
+
     boot.extraModulePackages = [
       config.boot.kernelPackages.rk818-charger  #< rk818 battery/charger isn't mainline as of 2024-10-01
       config.boot.kernelPackages.imx258  #< mainline imx258 camera driver has some power-on issues on PPP  (imx258 1-001a: Error reading reg 0x0016: -6)