add manual steps describing how to check launcher behavior regarding …

…POSIX signals

test/manual/Cardano/Launcher/POSIXSpec.md

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+# Cardano.Launcher.POSIX
+
+## Goal
+
+By default, the Haskell runtime and the `process` library we use to spawn new
+processes in the launcher don't catch `SIGTERM` signals on a unix system. This
+means that if we kill the launcher process, the sub-processes it has spawned
+will endure.
+
+What follows are steps which explains how to test that `SIGINT` and `SIGTERM`
+signals are correctly handled on a unix system.
+
+## Steps
+
+### `SIGINT`
+
+- Start the launcher using `stack exec -- cardano-wallet-launcher`
+- In another terminal, run `ps -ef | grep cardano`, there should be three
+  processes running (the launcher, the wallet and the underlying chain
+  producer)
+  ```
+  $ ps -ef | grep cardano
+  10983  4904  0 09:42 pts/1 00:00:00 /home/user/Documents/IOHK/cardano-wallet/.stack-work/install/x86_64-linux/lts-13.8/8.6.3/bin/cardano-wallet-launcher
+  11003 10983 75 09:42 pts/1 00:03:30 cardano-http-bridge start --port 8080
+  11071 10983 58 09:42 pts/1 00:02:41 cardano-wallet-server --wallet-server-port 8090 --http-bridge-port 8080 --network mainnet
+  ```
+
+- Send a `SIGINT` signal using by pressing `CTRL-C` in the first terminal
+- Run `ps -ef | grep cardano`, there's no more process running: the launcher,
+  the wallet and the chain producer have all stopped.
+
+### `SIGTERM`
+
+- Start the launcher in background using `stack exec -- cardano-wallet-launcher &`
+- Run `ps -ef | grep cardano` and lookup the `pid` of the launcher process (and
+  control that there are indeed three processes running: the launcher, the
+  wallet and the chain producer)
+  ```
+  $ ps -ef | grep cardano
+  10983  4904  0 09:42 pts/1 00:00:00 /home/user/Documents/IOHK/cardano-wallet/.stack-work/install/x86_64-linux/lts-13.8/8.6.3/bin/cardano-wallet-launcher
+  11003 10983 75 09:42 pts/1 00:03:30 cardano-http-bridge start --port 8080
+  11071 10983 58 09:42 pts/1 00:02:41 cardano-wallet-server --wallet-server-port 8090 --http-bridge-port 8080 --network mainnet
+  ```
+- Send a `SIGTERM` signal to this pid using `kill <pid>` 
+- Run `ps -ef | grep cardano`, there's no more process running: the launcher,
+  the wallet and the chain producer have all stopped.