[doc] Document Bazel-managed OpenOCD dependency
[doc] Document Bazel-managed OpenOCD dependency

Rather than editing incoming links to install_openocd.md, this commit
just edits install_openocd.md, which is kind of a cop out. Eventually,
we should rename the file to indicate that installation isn't a step you
need to worry about anymore.

Signed-off-by: Dan McArdle <8fb240f11ec935676fcfd8aed04f42f9ee63efa8@google.com>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan