[ZIP 32] clarify that path notation applies to any context

[daira]

We adapt the path notation of BIP 32 [#bip-0032] to describe shielded HD paths, using prime marks ($'$) to
indicate hardened derivation ($i' = i + 2^{31}$) as in BIP 44 [#bip-0044]:

• $\mathsf{CKDfvk}(\mathsf{CKDfvk}(\mathsf{CKDfvk}(m_\mathsf{Sapling}, a), b), c)$ is written as $m_\mathsf{Sapling} / a / b / c.$

This should say $\mathsf{CKDfvk}(\mathsf{CKDfvk}(\mathsf{CKDfvk}(m_\mathsf{Context}, a), b), c)$ is written as $m_\mathsf{Context} / a / b / c,$ where $\mathsf{Context}$ is $\mathsf{Sapling},$ $\mathsf{Orchard},$ or an arbitrary context.