Providing anchors for each option on the keytool man page can help when needing to reference an option from external documentation or content.

The javac page already does this: https://docs.oracle.com/en/java/javase/18/docs/specs/man/javac.html#option-class-path

Following its precedent and for consistency the anchors should follow the option-[option-name-in-lower-case] format, e.g. option-gencert.

For non-URL compliant characters in an option, if applicable, should be replaced with a `-`.