Add Atmel Studio integration known issues.

LUFA/DoxygenPages/KnownIssues.txt

@@ -37,6 +37,9 @@
   *    - No LUFA provided driver INF files for Windows are signed, and thus may fail to install on systems where driver signing is enforced (e.g. Windows 8).
   *  - Build System
   *    - No known issues.
+  *  - Atmel Studio Integration
+  *    - Not all devices are listed in the "Supported Parts" screen when selecting a device. To select an alternative device, change the "Show Device" drop-down to "All Parts".
+  *    - When switching boards after changing the device selection, a second conflicting BOARD symbol definition can be created that prevents successful compilation. To fix, open the project properties window (<i>Project->Project {name} Properties...</i> menu item), click the Toolchain tab, click "Symbols" under the "AVR/GNU C Compiler" section and remove the incorrect definition.
   *
   *  \section Sec_KnownIssues130303 Version 130303
   *  - AVR8 Architecture