Mention app: false on no app error

Author: José Valim

lib/mix/lib/mix/dep.ex

@@ -147,9 +147,10 @@ defmodule Mix.Dep do
     do: "ok"
 
   def format_status(%Mix.Dep{status: {:noappfile, path}}),
-    do: "could not find an app file at #{Path.relative_to_cwd(path)}, " <>
-        "this may happen when you specified the wrong application name in your deps " <>
-        "or if the dependency did not compile (which can be amended with `#{mix_env_var}mix deps.compile`)"
+    do: "could not find an app file at #{Path.relative_to_cwd(path)}. " <>
+        "This may happen if the dependency was not yet compiled, " <>
+        "or you specified the wrong application name in your deps, " <>
+        "or the dependency indeed has no app file (then you can pass app: false as option)"
 
   def format_status(%Mix.Dep{status: {:invalidapp, path}}),
     do: "the app file at #{Path.relative_to_cwd(path)} is invalid"