chore: point the placeholder homepage at the org wiki

The Cargo homepage feeds Plugin::URL, which hosts can show to users, so
the placeholder should be somewhere reachable rather than a github.com URL
that never existed.

This retires YOUR-USERNAME and YOUR-PLUGIN-NAME as canonical values, which
is the self-arming STALE mechanism working as designed: both were skipped
while they were part of HOMEPAGE and became live checks the moment they
were not. Both pass, since the whole URL was replaced.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WHt4DykxXaQnyaJfyS8KCn

Cargo.lock

@@ -1102,14 +1102,6 @@ dependencies = [
  "serde",
 ]
 
-[[package]]
-name = "nih_plug_template"
-version = "0.1.0"
-dependencies = [
- "nih_plug",
- "nih_plug_egui",
-]
-
 [[package]]
 name = "nih_plug_xtask"
 version = "0.1.0"
@@ -1502,6 +1494,14 @@ version = "0.2.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4596b6d070b27117e987119b4dac604f3c58cfb0b191112e24771b2faeac1a6"
 
+[[package]]
+name = "plugin_name"
+version = "0.1.0"
+dependencies = [
+ "nih_plug",
+ "nih_plug_egui",
+]
+
 [[package]]
 name = "polling"
 version = "3.11.0"