Parameters.md: update title and headings (#5420)
Parameters.md: update title and headings (#5420)

Be consistent about heading levels.
Will also help when inlining the file in other docs

arifogel/batfish,batfish/batfish,batfish/batfish,intentionet/batfish,arifogel/batfish,intentionet/batfish,dhalperi/batfish,dhalperi/batfish,intentionet/batfish,dhalperi/batfish,intentionet/batfish,arifogel/batfish,intentionet/batfish,batfish/batfish