docs: Add platform doc

Author: HofmeisterAn

docs/api/create_docker_container.md

@@ -2,6 +2,24 @@
 
 Testcontainers' generic container support offers the greatest flexibility and makes it easy to use virtually any container image in the context of a temporary test environment. To interact or exchange data with a container, Testcontainers provides `ContainerBuilder` to configure and create the resource.
 
+## Configure container image
+
+Use `WithImage(...)` to specify the container image.
+
+The simplest overload accepts a `string`:
+
+```csharp
+_ = new ContainerBuilder()
+  .WithImage("postgres:15.1");
+```
+
+For platform-specific scenarios, `WithImage` also accepts an `IImage`. Using the `DockerImage` implementation, you can explicitly set the platform:
+
+```csharp
+_ = new ContainerBuilder()
+  .WithImage(new DockerImage("postgres:15.1", "linux/amd64"));
+```
+
 ## Configure container start
 
 Both `ENTRYPOINT` and `CMD` allows you to configure an executable and parameters, that a container runs at the start. By default, a container will run whatever `ENTRYPOINT` or `CMD` is specified in the Docker container image. At least one of both configurations is necessary. The container builder implementation supports `WithEntrypoint(params string[])` and `WithCommand(params string[])` to set or override the executable. Ideally, the `ENTRYPOINT` should set the container's executable, whereas the `CMD` sets the default arguments for the `ENTRYPOINT`.

src/Testcontainers/Images/DockerfileArchive.cs

@@ -401,7 +401,7 @@ private static string ReplaceVariables(string line, IDictionary<string, string>
 
       if (quote != null)
       {
-        throw new FormatException($"Unmatched {quote} quote starting at position {start - 1} in line: '{line}'.");
+        throw new FormatException($"Unmatched {quote} quote in line: '{line}'.");
       }
 
       if (line.Length > start)
@@ -426,7 +426,7 @@ private static (string Name, string Value) ParseFlag(string flag)
       else
       {
         var name = trimmed.Substring(0, eqIndex);
-        var value = trimmed.Substring(eqIndex + 1).Trim(' ', '"', '\'');
+        var value = trimmed.Substring(eqIndex + 1).Trim().Trim('"', '\'');
         return (name, value);
       }
     }