[notary-project] updated folder name in pathspec to fix link

[MANISH-K-07]

howto was renamed to docs as part of https://github.com/cncf/techdocs/commit/b1b54b3a0b3de6ea9278104b796fcf1e794f9e21

There were a few pointer links hanging loose, this PR fixes the last of them.

https://github.com/cncf/techdocs/blob/main/howto/website-guidelines-checklist.md gives a 404 Changed to https://github.com/cncf/techdocs/blob/main/docs/website-guidelines-checklist.md

Relative urls can be used, but I've left the absolute url coz the rest of the links were absolute.