Update dev docs

README.md

@@ -24,6 +24,31 @@ Arch Linux has `libblst` in AUR, nix are exemplified by IOHK,
 and manual installation is described here:
 https://github.com/input-output-hk/cardano-node-wiki/blob/main/docs/getting-started/install.md#installing-blst
 
+## Running tests
+
+Tests depend on localdevnet, which is runned in Docker.
+To start it do:
+
+```bash
+./prepare-devnet.sh
+docker-compose  -f docker-compose.devnet.yaml up
+sudo chown -R $USER:$USER ./devnet/
+```
+
+After that run: `cabal test`.
+
+For development and fast response once could consider `ghcid`.
+
+## Devnet stalling bug
+
+Sometimes devnet stalls, due to some bug, in that case one should restart it,
+and wipe directory `./devnet/db`. To look for stalling one could check:
+`CARDANO_NODE_SOCKET_PATH=./devnet/node.socket cardano-cli query tip --testnet-magic 42`. For properly working devnet slots should change
+and sync be marked as 100%.
+
+On this bug:
+https://forum.cardano.org/t/restarting-custom-private-networks-cardano-node-forge35/116921
+
 ## Project status
 
 Project is in early development stage and is funded by