docs: improvement of the explanation of goss_wait.yaml (#1001)

* docs: improvement of the explanation of `goss_wait.yaml`

* fix md lint

extras/dcgoss/README.md

@@ -10,8 +10,14 @@ containers. It is based on `dgoss`.
 ### Run
 
 Run is used to validate a docker container defined in `docker-compose.yml`. It expects both a `docker-compose.yml`
-and `goss.yaml` file to exist in the directory it was invoked from. Container configuration is used from the
-compose file, for example:
+and `goss.yaml` file to exist in the directory it was invoked from.
+
+If the file `./goss_wait.yaml` exists in the current directory, goss regularly
+checks whether the conditions in the file are met. Only then does goss start the
+actual check with the file `./goss.yaml`. This is used, for example, to wait
+until a certain port is open before executing the tests.
+
+Container configuration is used from the compose file, for example:
 
 **run:**
 

extras/dgoss/README.md

@@ -47,6 +47,12 @@ dgoss run ...
 
 Run is used to validate a container.
 It expects a `./goss.yaml` file to exist in the directory it was invoked from.
+
+If the file `./goss_wait.yaml` exists in the current directory, goss regularly
+checks whether the conditions in the file are met. Only then does goss start the
+actual check with the file `./goss.yaml`. This is used, for example, to wait
+until a certain port is open before executing the tests.
+
 In most cases one can just substitute the runtime command (`docker` or `podman`)
 for the dgoss command, for example:
 

extras/kgoss/README.md

@@ -99,6 +99,11 @@ To find `goss.yaml` in another directory specify that directory's path in `GOSS_
 The `run` command is used to validate a container. It expects a
 `./goss.yaml` file to exist in the directory it was invoked from.
 
+If the file `./goss_wait.yaml` exists in the current directory, goss regularly
+checks whether the conditions in the file are met. Only then does goss start the
+actual check with the file `./goss.yaml`. This is used, for example, to wait
+until a certain port is open before executing the tests.
+
 **Example:**
 
 `kgoss run -e JENKINS_OPTS="--httpPort=8080 --httpsPort=-1" -e JAVA_OPTS="-Xmx1048m" -i jenkins:alpine`