Added section mentioning ARMC6 as the default ARM toolchains

Author: SenRamakri

docs/reference/configuration/mbed_targets.md

@@ -198,7 +198,9 @@ If you specify `ARMC5` in `supported_toolchains`, it means the corresponding tar
 
 If a target lists both `ARMC5` and `ARM` (or `ARMC6`) in `supported_toolchains`, the Arm Compiler 6.11 will be used when compiling with `ARM` option for `--toolchain`.
 
-<span class="notes">**Note:** Although you can specify `ARMC5` in `supported_toolchains` in `targets.json`, it's not a valid option for `--toolchain` when compiling using [Mbed CLI](../tools/developing-mbed-cli.html).</span>
+<span class="notes">**Note:** Although you can specify `ARMC5` in `supported_toolchains` in `targets.json`, it's not a valid option for `--toolchain` when compiling using [Mbed CLI](../tools/developing-mbed-cli.html).
+With Mbed-OS 5.12 release, ARM Compiler 6 will be the default ARM toolchain for Mbed-OS developmet. Majority of Mbed OS targets/platforms are already compatible with ARM Compiler 6. Some existing targets still using/supporting ARM Compiler 5 will also be migrated to ARM Compiler 6 in future. Please be aware that all new/existing Mbed OS targets/developers must use ARM Compiler 6 for future development and all code contributions to Mbed OS will be validated with ARM Compiler 6.
+</span>
 
 #### default_toolchain
 

docs/tools/tools_intro.md

@@ -38,7 +38,7 @@ The Mbed Online Compiler is our in-house IDE and should be familiar to anyone wh
 
 For more information, please see the [Online Compiler page](developing-mbed-online-compiler.html).
 
-<span class="note"> **Note:** With Mbed-OS 5.12 release, ARM Compiler 6 will be the default ARM toolchain for all Mbed OS targets. Majority of Mbed OS targets/platforms are already compatible with ARM Compiler 6. Few targets currently using/supporting ARM Compiler 5 will also be migrated to ARM Compiler in future. Please be aware that all new/existing Mbed OS targets/developers must use ARM Compiler 6 for future development and all code contributions to Mbed OS will be validated with ARM Compiler 6. </span>
+<span class="note"> **Note:** With Mbed-OS 5.12 release, ARM Compiler 6 will be the default ARM toolchain for Mbed-OS developmet. Majority of Mbed OS targets/platforms are already compatible with ARM Compiler 6. Some existing targets still using/supporting ARM Compiler 5 will also be migrated to ARM Compiler 6 in future. Please be aware that all new/existing Mbed OS targets/developers must use ARM Compiler 6 for future development and all code contributions to Mbed OS will be validated with ARM Compiler 6. </span>
 
 ##### Third party development tools