Add CLI tooling docs (#504)

Author: ErikSchierboom

building/config.json

@@ -820,6 +820,13 @@
     "title": "Snippet Extractor",
     "blurb": ""
   },
+  {
+    "uuid": "0d24b14c-8995-4ca5-8e5f-6ca2dcc5318c",
+    "slug": "tooling/cli",
+    "path": "building/tooling/cli.md",
+    "title": "Exercism CLI",
+    "blurb": ""
+  },
   {
     "uuid": "ba393f61-0f7d-4178-922a-c16cda052338",
     "slug": "tooling/test-generators",

building/tooling/cli.md

@@ -0,0 +1,22 @@
+# Exercism CLI
+
+The [Exercism CLI][cli] lets students download exercises and submit solutions to the site.
+It also supports the `exercism test` command, which then runs the track-specific command to run the tests.
+
+## Adding new language
+
+The track-specific test commands are defined in a [configuration file][test-configurations].
+You can add support for your language by adding an entry to that [configuration file][test-configurations], where the key is the track's slug.
+
+### Test command placeholders
+
+There are two placeholders that can be used in the track-specific command:
+
+- `{{test_files}}`: a space-separated list of the test files (as found in the `.files.test` key in the exercise's `.meta/config.json` file)
+- `{{solution_files}}`: a space-separated list of the solution files (as found in the `.files.solution` key in the exercise's `.meta/config.json` file)
+
+Here is an [example pull request][example-pr] that adds support for the Arturo language.
+
+[cli]: https://github.com/exercism/cli
+[example-pr]: https://github.com/exercism/cli/pull/1147/files
+[test-configurations]: https://github.com/exercism/cli/blob/main/workspace/test_configurations.go#L63

building/tracks/new/configure-tooling.md

@@ -1,8 +1,9 @@
 # Configure tooling
 
-There are two bits of tooling that you can optionally tweak for your track:
+There are three bits of tooling that you can optionally tweak for your track:
 
 - The **[Lines of Code Counter](/docs/building/tooling/lines-of-code-counter)**
 - The **[Snippet Extractor](/docs/building/tooling/snippet-extractor)**
+- The **[Exercism CLI](/docs/building/tooling/cli)**
 
 While tweaking these tools is optional, doing so can make your track's integration into the website just _that_ bit better.