[Docs] Move images into folder that gets pulled into public repo (#36008) (#36024)

These are broken links in the public repos, as the root images folder
isn't copied across. Good to keep them out of the root so moving to
`stdlib/docs/images` with the other images, to keep them out of the way.

modular-orig-commit: 4fbd0381ae221dde49ebcdce05de33739a42e8ed

Author: jackos

CONTRIBUTING.md

@@ -184,7 +184,7 @@ for more details.
 Go to the [Mojo repo](https://github.com/modularml/mojo) and click the fork
 button:
 
-![Create Fork](./images/create-fork.png)
+![Create Fork](stdlib/docs/images/create-fork.png)
 
 Clone your forked repo locally with the command:
 
@@ -249,7 +249,7 @@ If you're using bash, replace the three `~/.zshrc` above with `~/.bashrc`.
 Install the [Mojo nightly VS Code
 extension](https://marketplace.visualstudio.com/items?itemName=modular-mojotools.vscode-mojo-nightly):
 
-<img src="./images/nightly-extension.png" width=350 />
+<img src="./stdlib/docs/images/nightly-extension.png" width=350 />
 
 You can only have one Mojo extension enabled at a time, remember to switch back
 when using the stable release!
@@ -275,7 +275,7 @@ remote:      https://github.com/jackos/mojo/pull/new/my-fix-pr
 
 Make sure you point it to the `nightly` branch:
 
-![Base Branch](images/base-branch.png)
+![Base Branch](stdlib/docs/images/base-branch.png)
 
 Now fill out the details:
 

stdlib/docs/development.md

@@ -305,7 +305,7 @@ error: CHECK: expected string not found in input
 
 Lets fix the test that we just added:
 
-```plaintext
+```mojo
 # CHECK-LABEL: test_print_cwd
 
 def test_print_cwd():