Review comments fixes for compiler override docs

Author: SenRamakri

docs/tools/tools_intro.md

@@ -21,7 +21,8 @@ We created the Mbed command-line tool (Mbed CLI), a Python-based tool, specifica
 
 Mbed OS 5 can be built with various toolchains. The currently supported versions are:
 
-- [Arm compiler 6.11](https://developer.arm.com/products/software-development-tools/compilers/arm-compiler/downloads/version-6).
+- [Arm compiler 6.11 (default ARM toolchain)](https://developer.arm.com/products/software-development-tools/compilers/arm-compiler/downloads/version-6).
+- [Arm compiler 5.06 update 6 (to be deprecated in the future)](https://developer.arm.com/products/software-development-tools/compilers/arm-compiler-5/downloads).
 - [GNU Arm Embedded version  6 (6-2017-q1-update)](https://developer.arm.com/open-source/gnu-toolchain/gnu-rm/downloads).
 - [IAR Embedded Workbench 8.32.1](https://www.iar.com/iar-embedded-workbench/tools-for-arm/arm-cortex-m-edition/).
 
@@ -78,5 +79,4 @@ See below for example:
 }
 ```
 
-<span class="note"> **Note:** The above methods to override ARM toolchain version is made available only to enable developers migrating from ARM Compiler 5 to ARM Compiler 6. Future releases of Mbed OS may remove
-this option and thus developers are strongly encouraged to move to ARM Compiler 6.</span>
+<span class="note"> **Note:** The above methods to override ARM toolchain version is made available only to enable developers migrating from ARM Compiler 5 to ARM Compiler 6. We encourage developers to make plans to switch to ARM Compiler 6 soon, as we plan to deprecate ARM Compiler 5 support in the future and this migration would ensure that your software is compatible with it. </span>