Add links in CONTRIBUTING.md

This would help people to find explanation or reuse an existing issue
when implementing it.

CONTRIBUTING.md

@@ -179,6 +179,7 @@ Describe a new checker in [checkers section](./README.md#checkers).
 **Autofix**: false. <br>
 **Enabled by default**: true. <br>
 **Reason**: The `Error()` method on the `error` interface exists for humans, not code.
+**Related issues**: #47
 
 ---
 
@@ -312,13 +313,15 @@ And similar idea for `assert.InEpsilonSlice` / `assert.InDeltaSlice`.
 **Autofix**: true. <br>
 **Enabled by default**: maybe? <br>
 **Reason**: More appropriate `testify` API with clearer failure message.
+**Related issues**: #76
 
 ---
 
 ### no-fmt-mess
 
 **Autofix**: true. <br>
 **Enabled by default**: maybe?
+**Related issues**: #33
 
 Those who are new to `testify` may be discouraged by the duplicative API:
 
@@ -471,6 +474,7 @@ assert.ErrorContains(t, err, "user") ❌
 **Autofix**: true. <br>
 **Enabled by default**: false. <br>
 **Reason**: Just for your reflection and suggestion.
+**Related issues**: #75
 
 I'm not sure if anyone uses `assert.Zero` – it looks strange and conflicts with `assert.Empty`: