add assert

Author: andrewrosemberg

docs/make.jl

@@ -10,6 +10,8 @@ plutos = [
     joinpath(repo_dir, "class01", "background_materials", "basics_math.jl"),
 ]
 
+@assert isfile(repo_dir, "docs", "class01.md") "Expected docs/class01.md to exist."
+
 makedocs(
     sitename = "LearningToControlClass",
     format = Documenter.HTML(;
@@ -24,7 +26,7 @@ makedocs(
     ),
     pages  = [
         "Home"   => "index.md",
-        "Class 1" => "class01/class01.md",
+        "Class 1" => "class01.md",
     ],
 )