Fix wrong CMake variable name in docs

Author: dariusarnold

.devcontainer.json

@@ -5,6 +5,9 @@
 		"dockerfile": "docker/Dockerfile",
 		"context": "docker",
 	},
+    "mounts": [
+      "source=infinitime-bashhistory,target=/commandhistory,type=volume"
+    ],
 	"customizations": {
 		"vscode": {
 			"settings": {

cmake-nRF5x/readme.md

@@ -105,7 +105,7 @@ After setup you can use cmake as usual:
 	```
 	You can optionally pass the toolchain to `cmake` when configuring:
     ```
-    -DCMAKE_TOOLCHAIN_PATH=cmake-nRF5x/arm-gcc-toolchain.cmake
+    -DCMAKE_TOOLCHAIN_FILE=cmake-nRF5x/arm-gcc-toolchain.cmake
     ```
     but if you do so you must ensure the toolchain binaries are available in your environment PATH (i.e. work on the command line without specifying absolute path)