docs: Add expirydate to front-matter doc
docs: Add expirydate to front-matter doc

abourget/hugo,abourget/hugo,gohugoio/hugo,anthonyfok/hugo,fedelibre/hugo,mitchchn/hugo,MarkDBlackwell/hugo,vbatoufflet/hugo,ffrizzo/hugo,anthonyfok/hugo,tischda/hugo,jygastaud/hugo,mitchchn/hugo,fedelibre/hugo,digitalcraftsman/hugo,mdhender/hugo,tubo028/hugo,MarkDBlackwell/hugo,gohugoio/hugo,Zenithar/hugo,mayah/hugo,ffrizzo/hugo,mdhender/hugo,mdhender/hugo,tubo028/hugo,tischda/hugo,fedelibre/hugo,bogem/hugo,vbatoufflet/hugo,jygastaud/hugo,gohugoio/hugo,digitalcraftsman/hugo,anthonyfok/hugo,melo/hugo,mdhender/hugo,bogem/hugo,fedelibre/hugo,Zenithar/hugo,mayah/hugo,melo/hugo