fix broken links (#20)

* fix broken links

* remove non-existing link

.github/workflows/ci.yml

@@ -0,0 +1,18 @@
+name: CI
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  check-links:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@main
+      - name: Markup Link Checker (mlc)
+        uses: becheran/mlc@v0.15.4
+        with:
+          args: --no-web-links

block.md

@@ -166,7 +166,7 @@ Below is an example of block profile encoded in [pprof's protobuf format](./ppro
 - contentions/count
 - delay/nanoseconds
 
-The `blockprofilerate` used to create the profile is not included, neither are [profiler labels](./profiler-labels).
+The `blockprofilerate` used to create the profile is not included, neither are profiler labels.
 
 ```
 $ go tool pprof -raw block.pb.gz 

examples/block-net/README.md

@@ -1,6 +1,6 @@
 # block-net
 
-This [program](./main.go) explores the [question](https://twitter.com/rogpeppe/status/1359202847708037124) whether network i/o (e.g. waiting on socket read/write operations) will show up in the [block profiler](/block.md) or not.
+This [program](./main.go) explores the [question](https://twitter.com/rogpeppe/status/1359202847708037124) whether network i/o (e.g. waiting on socket read/write operations) will show up in the [block profiler](../../block.md) or not.
 
 The program does the following:
 
@@ -22,5 +22,5 @@ However, as you can see below, the block profiler [captures](./block.pb.gz) only
 
 ![block-net](./block-net.png)
 
-This means that [block profiler](/block.md) is generally not able to give a good idea about goroutines that are waiting on network i/o. 
+This means that [block profiler](../../block.md) is generally not able to give a good idea about goroutines that are waiting on network i/o.