Side notes for users not seeing matching output

For readers who have not used the Determinate Nix Installer, they'll probably
need to activate the nix command and flakes, and they may not get the change
in command prompt in entry 3. This is the case if someone is using the official
installer or trying to read through the guide on nixos. Closes DeterminateSystems#315.

Author: ammkrn

src/pages/start/2.nix-run.mdx

@@ -27,6 +27,13 @@ This is in contrast to most [package managers][pkg], which install things more q
 Future `nix run` invocations should be instantaneous, as Nix doesn't need to build the package again.
 </Admonition>
 
+<Admonition warning title="If you installed nix on your own" id="nix-run-loading" client:load>
+If you installed Nix by means other than the [Determinate Nix Installer][nix-installer], you'll probably need to manually enable the nix command and flakes 
+(if you're seeing an error about experimental features, this it you). you can find out how to activate those features on their respective Nix wiki 
+pages: see [nix command](https://nixos.wiki/wiki/Nix_command) and [flakes](https://nixos.wiki/wiki/Flakes).
+</Admonition>
+
+
 ## Explanation
 
 What happened here? The [Nix] CLI did a few things:

src/pages/start/3.nix-develop.mdx

@@ -42,6 +42,12 @@ type curl
 type git
 ```
 
+If your shell prompt didn't change, you should still be able to tell something happened by checking the `FUNNY_JOKE` variable added by the 
+development environment we just activated:
+```shell
+echo $FUNNY_JOKE
+```
+
 For curl, for example, you should see a strange path like this (the hash part should be different on your machine):
 
 <NixStorePath pkg="curl-8.1.1-bin" bin="curl" />