doc/tools: document gitea-cli configuration

Makefile

@@ -90,7 +90,16 @@ test_kvm_uefi:
 
 # Update TODO.md by fetching issues from the main gitea instance API
 # requirements: sudo apt install git jq
-#               gitea-cli config defined in ~/.config/gitearc
+#               gitea-cli config defined in ~/.config/gitearc:
+# GITEA_USER=user
+# GITEA_API_TOKEN=token
+# GITEA_URL=https://git.example.org
+# # Allow self-signed certs
+# curl() { command curl --insecure "$@"; }
+# gitea.issues() {
+# 	split_repo "$1"
+# 	auth curl --silent "${GITEA_URL%/}/api/v1/repos/$REPLY/issues"
+# }
 update_todo:
 	git clone https://github.com/bashup/gitea-cli gitea-cli
 	echo '<!-- This file is automatically generated by "make update_todo" -->' >| doc/md/TODO.md