fix stale example link in README, add lychee link checker to CI

Signed-off-by: PeaBrane <peabrane@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: PeaBrane

.github/workflows/ci.yml

@@ -6,6 +6,15 @@ on:
   pull_request:
 
 jobs:
+  links:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: lycheeverse/lychee-action@v2
+        with:
+          args: --no-progress '**/*.md'
+          fail: true
+
   check:
     runs-on: ubuntu-latest
     steps:

README.md

@@ -63,7 +63,7 @@ tri.sample(n_sweeps=5000, sweep_mode="metropolis",
 print(tri.binder_cumulant)
 ```
 
-For a more complete example, check out [example.py](example.py).
+For a more complete example, check out [examples/energy_vs_temperature.py](examples/energy_vs_temperature.py).
 
 ## Installation