doc: Installation Guide "C++ runtime" section

[lleaver]

Please also confirm the following

• I have searched the main issue tracker of NeMo Guardrails repository and believe that this is not a duplicate

Issue Kind

Improving documentation

Existing Link

https://docs.nvidia.com/nemo/guardrails/latest/getting-started/installation-guide.html

Description

The section titled "Installing a C++ runtime on Linux, Mac, or Unix-based OS" appears as a prominent header in the NeMo Guardrails Installation Guide. This placement is a bit confusing, as upon first glance it appears to be a required manual step for all installations, even though it is only needed for troubleshooting certain environments. Moving it to a dedicated "Troubleshooting" section after the main "pip install nemoguardrails" instructions with a smaller header would help to make the instructions simpler and more clear.