Add shadowenv prompt-widget mention to docs

Author: burke

docs/best-practices.md

@@ -39,3 +39,9 @@ a locally-generated artifact and be generated entirely by user tooling. At Shopi
 
 This is not the only valid way to go though, you may get some mileage out of committing the files.
 Let us know what you do!
+
+## Propmt Widget
+
+You may find it helpful to have a visual indicator in your terminal that a
+Shadowenv is active. You can embed `$(shadowenv prompt-widget)` in your `PS1` or
+`PROMPT`, etc., to achieve this.

docs/getting-started.md

@@ -132,3 +132,16 @@ shadowenv exec -- nginx -g 'daemon off;'
 
 In this case, we didn't need to load the Shadowenv shell hook, as `shadowenv exec` loaded the
 environments before executing nginx.
+
+# Nested Shadowenvs
+
+Shadowenv supports nested environments. In order for a shadowenv to inherit from
+another shadowenv further up the path, create a symlink at
+`.shadowenv.d/parent` to the higher `.shadowenv.d`. For example:
+
+```
+ln -s /a/.shadowenv.d /a/b/c/.shadowenv.d/parent
+```
+
+When this is done, shadowlisp files in `a` will be evaluated before those in
+`c`.