docs: add steps to recreate deno lock file

README.md

@@ -6,6 +6,8 @@ It is built using [lume](https://lume.land/) with JSX. To get started, make sure
 you have the [nix package manager](https://nixos.org/download.html) installed.
 Then you can start developing with:
 
+### Quick start
+
 ```
 nix develop
 ```
@@ -38,3 +40,16 @@ To update the font files and CSS, run `google-font-downloader $FONT_CSS_URL`.
 As "documentation" `flake.nix` shows the internals, and
 `_includes/styles/typography.css` has a comment at the top that shows which
 command was used to generate it.
+
+### Troubleshooting
+An common error is:
+
+```
+22.31 error: The source code is invalid, as it does not match the expected hash in the lock file.
+```
+
+To recreate the deno lock file, run
+
+```
+deno cache --lock=deno.lock --lock-write _config.ts
+```