doc: update list of supported architectures

- Add MIPS to the list.
- Update ARC entry with ARCv3 support.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

doc/introduction/index.rst

@@ -9,7 +9,7 @@ sensors and LED wearables to sophisticated embedded controllers, smart
 watches, and IoT wireless applications.
 
 The Zephyr kernel supports multiple architectures, including:
- - ARC EM and HS
+ - ARCv2 (EM and HS) and ARCv3 (HS6X)
  - ARMv6-M, ARMv7-M, and ARMv8-M (Cortex-M)
  - ARMv7-A and ARMv8-A (Cortex-A, 32- and 64-bit)
  - ARMv7-R, ARMv8-R (Cortex-R, 32- and 64-bit)
@@ -18,6 +18,7 @@ The Zephyr kernel supports multiple architectures, including:
  - RISC-V (32- and 64-bit)
  - SPARC V8
  - Tensilica Xtensa
+ - MIPS (MIPS32 Release 1 specification)
 
 The full list of supported boards based on these architectures can be found :ref:`here <boards>`.