ci: add a simple line length tool to check docs.md

cmd/tools/check-md.v

@@ -0,0 +1,31 @@
+module main
+
+import os
+
+const (
+	too_long_line_length = 100
+)
+
+fn main() {
+	files_paths := os.args[1..]
+	mut errors := 0
+	for file_path in files_paths {
+		real_path := os.realpath(file_path)
+		lines := os.read_lines(real_path) or {
+			continue
+		}
+		for i, line in lines {
+			if line.len > too_long_line_length {
+				eprintln('$real_path:${i+1}:${line.len+1}: line too long')
+				errors++
+			}
+		}
+	}
+	// TODO: uncomment this AFTER doc/docs.md line lengths are fixed
+	/*	
+	if errors > 0 {
+		exit(1)
+	}
+	*/
+
+}