[DG] Fix how to run path

Description

Path under How To Run section is refering the old struct where the doc-gen tool was under the general cadence repo

[x] Targeted PR against master branch
[ ] Linked to Github issue with discussion and accepted design OR link to spec that describes this work
[x] Code follows the standards mentioned here
[x] Updated relevant documentation
[x] Re-reviewed Files changed in the Github PR explorer
[ ] Added appropriate labels