Help on macaulay2_console should document this is optional

[drkirkby]

Running:

sage: macaulay2_console()
sh: line 1: M2: not found

gives that above error message, but the help page does not document this is an optional program, and not part of Sage.

sage: help(macaulay2_console)

macaulay2_console()
    Spawn a new M2 command-line session.
    
    EXAMPLES:
        sage: macaulay2_console()                    # not tested
        Macaulay 2, version 1.1
        with packages: Classic, Core, Elimination, IntegralClosure, LLLBases, Parsing, PrimaryDecomposition, SchurRings, TangentCone
        ...

Related: #11710 (Macaulay2 build error; perhaps upgrading the package)