Document builtins.appendContext

[PkmX]

Problem

While trying to string together the lost context due to #2547, I had to look up the argument order of the built-in function appendContext in the source code

The appendContext built-in is also mentioned in the document:

nix/doc/manual/src/language/string-context.md

Line 125 in 09199a4

[`builtins.appendContext`] will create a copy of a string, but with additional string context elements.

But it is not documented:

nix/src/libexpr/primops/context.cc

Line 326 in 09199a4

static RegisterPrimOp primop_appendContext({

Proposal

Document the builtins.appendContext.

Checklist

• checked latest Nix manual (source)
• checked open documentation issues and pull requests for possible duplicates

Priorities

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