Updated troubleshooting documentation

Focuses on issues experienced related to the macOS Big Sur upgrade.

README.adoc

@@ -195,6 +195,12 @@ link:https://www.alchemists.io/projects/mac_os-config[macOS Config] project for
 
 == Troubleshooting
 
+* When using link:https://pi-hole.net[Pi-hole], make sure to temporarily disable prior to upgrading
+  as you might experience various errors with Apple not able to detect an internet connection which
+  prevents the installer from working.
+* When using the boot disk and the installer fails in some catestrophic manner, reboot the machine
+  into recovery mode (i.e. `COMMAND + R`) to download and install the last operating system used.
+  You can also use `COMMAND + OPTION + R` to attemp to download the latest operating system.
 * When using the boot disk, you might experience a situation where you see a black screen with a
   white circle and diagonal line running through it. This means macOS lost or can’t find the boot
   disk for some reason. To correct this, shut down and boot up the system again while holding down
@@ -202,13 +208,6 @@ link:https://www.alchemists.io/projects/mac_os-config[macOS Config] project for
   happen a few times before releasing the keys. This will clear the system NVRAM/PRAM. At this point
   you can shut down and restart the system following the boot disk instructions (the boot disk will
   be recognized now).
-* Sometimes, when installing XCode development tools (i.e. the `t` option), not all of the macOS
-  headers will be installed. This can cause issues with compiling and building native packages. For
-  example: `fatal error: 'stdio.h' file not found`. This can happen due to an intermittent bug with
-  the XCode installer. To fix this, you’ll need to install this package:
-  `/Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg`. Depending on
-  your system, the version might differ, so look for a `*.pkg` in the
-  `/Library/Developer/CommandLineTools/Packages` folder.
 
 == Development