OSAL Configuration Guide Link is broken in README

[rosspeters6]

Describe the bug
The link to the OSAL Configuration Guide is broken in blob/main/README.md.

To Reproduce
Go to https://github.com/nasa/osal/blob/main/README.md and then click on the "Configuration Guide" link near the bottom of the file. It navigates to the old PDF file link.

Expected behavior
I expected the link to take me to the Markdown file in the repo.

Code snips
See the [Configuration Guide](https://github.com/nasa/osal/blob/master/doc/OSAL-Configuration-guide.pdf) for more information. (should reference doc/OSAL-Configuration-Guide.md).

System observed on:
Documentation only.

Additional context
N/A

Reporter Info
Ross Peters