Add section to CONFIGURE.md link

[iyanmv]

This is a very small change so that ninja gen_docs works as expected.

Without this change, doxygen (at least, version 1.9.8) gives the following error:

unable to resolve reference to '/liboqs/CONFIGURE.md' for \ref command

This makes scripts/run_doxygen.sh return exit code 1 instead of 0, and causes ninja gen_docs to fail

• Does this PR change the input/output behaviour of a cryptographic algorithm (i.e., does it change known answer test values)? (If so, a version bump will be required from x.y.z to x.(y+1).0.)
• Does this PR change the list of algorithms available -- either adding, removing, or renaming? Does this PR otherwise change an API? (If so, PRs in oqs-provider, OQS-OpenSSL, OQS-BoringSSL, and OQS-OpenSSH will also need to be ready for review and merge by the time this is merged.)

[baentsch]

LGTM. Thanks for the contribution!