MUST we not use SHALL?

[garethsb]

We include all the conformance key words of RFC 2119 in the template

bcp-template/docs/Overview.md

Lines 42 to 43 in 2567ecc

	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
	and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119][RFC-2119].

But we invariably use MUST rather than SHALL in all NMOS specs, in opposition to the VSF who seem to always use SHALL.
Should we add a line guiding spec authors?