update doc

README.md

@@ -42,7 +42,22 @@ source /opt/profile/profile.sh
 It's not recommended to load that profile in `/etc/profile` as users' `.bashrc`
 files might interfere with some aliases and functions defined in profile.
 
-### 2.1. Initial configuration
+### 2.1. Interactive vs non-interactive shells
+
+`profile.sh` detects whether the current shell is interactive.
+
+In interactive shells (typical terminal sessions), profile enables
+interactive-only features such as:
+- aliases from `[aliases]`
+- bash completion scripts from `profile.d/bash-completion/`
+- prompt initialization (`PROMPT_COMMAND` and timer hook)
+- welcome display (`showinfo`) and startup update check (`check_updates -q`)
+
+In non-interactive shells (typical script execution), those features are
+intentionally skipped to avoid side effects and startup noise. Public functions
+remain available after sourcing, so scripts can still call profile helpers.
+
+### 2.2. Initial configuration
 Copy the example configuration file and customise it to your needs:
 ```bash
 cp <installpath>/profile/doc/profile.conf.example <installpath>/profile/profile.conf
@@ -132,7 +147,7 @@ apply when unset.
 
 `profile.conf` is listed in `.gitignore` so personal values (API keys, cities,
 compiler flags, …) are never accidentally staged. Start from the annotated
-template at `doc/profile.conf.example` (see [section 2.1](#21-initial-configuration)).
+template at `doc/profile.conf.example` (see [section 2.2](#22-initial-configuration)).
 
 ### 4.1. Core sections