docs(features): add more content on exec function

docs/features/override_container_command.md

@@ -1,7 +1,9 @@
-# Sending a CMD to a Container
+# Executing commands
 
-If you would like to send a CMD (command) to a container, you can pass it in to
-the container request via the `Cmd` field...
+## Container startup command
+
+By default the container will execute whatever command is specified in the image's Dockerfile. If you would like to send a CMD (command) to a container, you can pass it in to
+the container request via the `Cmd` field. For example:
 
 ```go
 req := ContainerRequest{
@@ -13,3 +15,68 @@ req := ContainerRequest{
 }
 ```
 
+## Executing a command
+
+You can execute a command inside a running container, similar to a `docker exec` call:
+
+```go
+func TestIntegrationNginxLatestReturn(t *testing.T) {
+    ctx := context.Background()
+    req := ContainerRequest{
+    Image: "docker.io/busybox",
+        Cmd:   []string{"sleep", "10"},
+           Tmpfs: map[string]string{"/testtmpfs": "rw"},
+    }
+
+    container, err := GenericContainer(ctx, GenericContainerRequest{
+        ContainerRequest: req,
+        Started:          true,
+    })
+
+    require.NoError(t, err)
+
+    t.Cleanup(func() {
+        t.Log("terminating container")
+        require.NoError(t, container.Terminate(ctx))
+    })
+
+    path := "/testtmpfs/test.file"
+
+    c, _, err := container.Exec(ctx, []string{"ls", path})
+    if err != nil {
+        t.Fatal(err)
+    }
+}
+```
+
+This can be useful for software that has a command line administration tool. You can also get the logs of the command execution (from an object that implements the [io.Reader](https://pkg.go.dev/io#Reader) interface). For example:
+
+```go
+import (
+    "fmt"
+	"io"
+	"log"
+	"strings"
+    "testing"
+)
+
+func TestIntegrationNginxLatestReturn(t *testing.T) {
+    // ...
+
+    c, reader, err := container.Exec(ctx, []string{"ls", path})
+    if err != nil {
+        t.Fatal(err)
+    }
+
+    buf := new(strings.Builder)
+    _, err := io.Copy(buf, reader)
+    if err != nil {
+        t.Fatal(err)
+    }
+
+    // See the logs of the command execution.
+    t.Log(buf.String())
+}
+```
+
+This is done this way, because it brings more flexibility to the user, rather than returning a string.