Add explanation

Signed-off-by: zeramorphic <[email protected]>

.docker/gitpod/Dockerfile

@@ -1,6 +1,10 @@
 # This is the Dockerfile for `leanprovercommunity/mathlib:gitpod`.
 # As well as elan and mathlib, we also install leanblueprint and all of its dependencies.
 
+# This container does not come with a pre-installed version of mathlib.
+# When a gitpod container is spawned, elan will be updated and mathlib will be downloaded:
+# see the .gitpod.yml file for more information.
+
 FROM ubuntu:jammy
 
 USER root

.docker/mathlib/Dockerfile

@@ -1,7 +1,10 @@
 # This is the Dockerfile for `leanprovercommunity/mathlib`.
 # It is based on the `leanprovercommunity/lean` image.
-# This Dockerfile doesn't contain a copy of mathlib;
+
+# This container does not come with a pre-installed version of mathlib;
 # you should call `lake exe cache get` which will download the most recent version.
+# The only difference between this Dockerfile and leanprovercommunity/lean is that this image
+# bypasses a warning that could occur when trying to connect to github for the first time.
 
 FROM leanprovercommunity/lean:debian