Fix links in docs. (#2556)

polkadot/roadmap/implementers-guide/src/node/availability/availability-distribution.md

@@ -46,11 +46,8 @@ backers, not all of them are required to have the needed chunk. This in turn
 could lead to low throughput, as we have to wait for a fetches to fail,
 before reaching a validator finally having our chunk. We do rank back validators
 not delivering our chunk, but as backers could vary from block to block on a
-perfectly legitimate basis, this is still not ideal. See the following issues
-for more information:
-
-https://github.com/paritytech/polkadot/issues/2509
-https://github.com/paritytech/polkadot/issues/2512
+perfectly legitimate basis, this is still not ideal. See issues [2509](https://github.com/paritytech/polkadot/issues/2509) and [2512](https://github.com/paritytech/polkadot/issues/2512)
+for more information.
 
 The current implementation also only fetches chunks for occupied cores in blocks
 in active leaves. This means though, if active leaves skips a block or we are