Add documentation for gt, the Gitea CLI (#603)

Adds a CLI product for gt (https://gitea.com/gitea/cli), set up like the runner, with short guides for installation, logging in, CI and scripting. Each command's details stay in gt <command> --help. Until the first release, the docs are served at /cli/; make cut-version PRODUCT=cli VERSION=0.1 adds the release series.

Closes https://gitea.com/gitea/cli/issues/16

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Co-authored-by: silverwind <[email protected]>
Reviewed-on: https://gitea.com/gitea/docs/pulls/603
Reviewed-by: Lunny Xiao <[email protected]>
Reviewed-by: silverwind <[email protected]>

cli-sidebars.js

@@ -0,0 +1,16 @@
+// Sidebar of the gt (Gitea CLI) documentation (develop version).
+// Released versions carry their own copy in
+// cli-docs_versioned_sidebars/version-<version>-sidebars.json.
+module.exports = {
+  cli: [
+    {
+      type: 'doc',
+      id: 'index',
+      label: 'What is gt?',
+    },
+    'installation',
+    'authentication',
+    'ci',
+    'scripting',
+  ],
+};