Build process crashes when - path: docs/README.md is specified

[mscno]

The build process crashes and panics when specifying the README.md file as a path.

Example:

// >> doctave.yaml
---
title: "Repo"
navigation:
  - path: docs/README.md

$ RUST_BACKTRACE=1 doctave build                                                                                                                                                                                                

at 14:37:03
Doctave | Build
Building site into /home/msc/Code/go/src/oceanbolt.com/spire-vessels/site

thread 'main' panicked at 'No matching link found', src/navigation.rs:47:26
stack backtrace:
   0: rust_begin_unwind
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/panicking.rs:92:14
   2: core::option::expect_failed
             at /rustc/c8dfcfe046a7680554bf4eb612bad840e7631c4b/library/core/src/option.rs:1578:5
   3: doctave::navigation::Navigation::customize
   4: doctave::navigation::Navigation::build_for
   5: <doctave::site::DiskBackedSite as doctave::site::Site>::build
   6: doctave::build::BuildCommand::run
   7: doctave::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

It is not a major issue, but it caused a bit of debugging for me trying to get the custom navigation to work. It was unclear that it was the README.md inclusion that caused the error. Suggesting to either ignore the file if specified, or provide a more helpful error.

[begleynk]

Ah thanks for reporting this. Looks like I've missed a unit test case.