doc: use .md extension for internal links

This helps catch broken links as part of the test suite. This also
improves the user experience when browsing the markdown files.

PR-URL: https://github.com/nodejs/node/pull/35191
Fixes: https://github.com/nodejs/node/issues/35189
Reviewed-By: Derek Lewis <DerekNonGeneric@inf.is>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

1 files changed, 56 insertions, 56 deletions

diff --git a/doc/api/index.md b/doc/api/index.md
index aad731f2b94..aadd5b4c794 100644
--- a/doc/api/index.md
+++ b/doc/api/index.md
@@ -5,65 +5,65 @@
 
 <!--introduced_in=v0.10.0-->
 
-* [About this documentation](documentation.html)
-* [Usage and example](synopsis.html)
+* [About this documentation](documentation.md)
+* [Usage and example](synopsis.md)
 
 <hr class="line"/>
 
-* [Assertion testing](assert.html)
-* [Async hooks](async_hooks.html)
-* [Buffer](buffer.html)
-* [C++ addons](addons.html)
-* [C/C++ addons with N-API](n-api.html)
-* [C++ embedder API](embedding.html)
-* [Child processes](child_process.html)
-* [Cluster](cluster.html)
-* [Command-line options](cli.html)
-* [Console](console.html)
-* [Crypto](crypto.html)
-* [Debugger](debugger.html)
-* [Deprecated APIs](deprecations.html)
-* [DNS](dns.html)
-* [Domain](domain.html)
-* [Errors](errors.html)
-* [Events](events.html)
-* [File system](fs.html)
-* [Globals](globals.html)
-* [HTTP](http.html)
-* [HTTP/2](http2.html)
-* [HTTPS](https.html)
-* [Inspector](inspector.html)
-* [Internationalization](intl.html)
-* [Modules: CommonJS modules](modules.html)
-* [Modules: ECMAScript modules](esm.html)
-* [Modules: `module` API](module.html)
-* [Modules: Packages](packages.html)
-* [Net](net.html)
-* [OS](os.html)
-* [Path](path.html)
-* [Performance hooks](perf_hooks.html)
-* [Policies](policy.html)
-* [Process](process.html)
-* [Punycode](punycode.html)
-* [Query strings](querystring.html)
-* [QUIC](quic.html)
-* [Readline](readline.html)
-* [REPL](repl.html)
-* [Report](report.html)
-* [Stream](stream.html)
-* [String decoder](string_decoder.html)
-* [Timers](timers.html)
-* [TLS/SSL](tls.html)
-* [Trace events](tracing.html)
-* [TTY](tty.html)
-* [UDP/datagram](dgram.html)
-* [URL](url.html)
-* [Utilities](util.html)
-* [V8](v8.html)
-* [VM](vm.html)
-* [WASI](wasi.html)
-* [Worker threads](worker_threads.html)
-* [Zlib](zlib.html)
+* [Assertion testing](assert.md)
+* [Async hooks](async_hooks.md)
+* [Buffer](buffer.md)
+* [C++ addons](addons.md)
+* [C/C++ addons with N-API](n-api.md)
+* [C++ embedder API](embedding.md)
+* [Child processes](child_process.md)
+* [Cluster](cluster.md)
+* [Command-line options](cli.md)
+* [Console](console.md)
+* [Crypto](crypto.md)
+* [Debugger](debugger.md)
+* [Deprecated APIs](deprecations.md)
+* [DNS](dns.md)
+* [Domain](domain.md)
+* [Errors](errors.md)
+* [Events](events.md)
+* [File system](fs.md)
+* [Globals](globals.md)
+* [HTTP](http.md)
+* [HTTP/2](http2.md)
+* [HTTPS](https.md)
+* [Inspector](inspector.md)
+* [Internationalization](intl.md)
+* [Modules: CommonJS modules](modules.md)
+* [Modules: ECMAScript modules](esm.md)
+* [Modules: `module` API](module.md)
+* [Modules: Packages](packages.md)
+* [Net](net.md)
+* [OS](os.md)
+* [Path](path.md)
+* [Performance hooks](perf_hooks.md)
+* [Policies](policy.md)
+* [Process](process.md)
+* [Punycode](punycode.md)
+* [Query strings](querystring.md)
+* [QUIC](quic.md)
+* [Readline](readline.md)
+* [REPL](repl.md)
+* [Report](report.md)
+* [Stream](stream.md)
+* [String decoder](string_decoder.md)
+* [Timers](timers.md)
+* [TLS/SSL](tls.md)
+* [Trace events](tracing.md)
+* [TTY](tty.md)
+* [UDP/datagram](dgram.md)
+* [URL](url.md)
+* [Utilities](util.md)
+* [V8](v8.md)
+* [VM](vm.md)
+* [WASI](wasi.md)
+* [Worker threads](worker_threads.md)
+* [Zlib](zlib.md)
 
 <hr class="line"/>