Add documentation for OpenAI feature

.env.example

@@ -2,4 +2,6 @@ NEXT_PUBLIC_POSTHOG_KEY=
 NEXT_PUBLIC_POSTHOG_HOST=
 
 NEXT_PUBLIC_SUPABASE_URL=
-NEXT_PUBLIC_SUPABASE_ANON_KEY=
+NEXT_PUBLIC_SUPABASE_ANON_KEY=
+
+OPENAI_API_KEY=

README.md

@@ -67,6 +67,8 @@ For user authentication, the project uses Supabase.
 
 For analytics, the project uses PostHog.
 
+To explain questions, the project uses the OpenAI API.
+
 You will need to create accounts for these services and set up projects to get the required environment variables.
 
 ## Environment Variables
@@ -81,6 +83,8 @@ The following environment variables are required:
 - `NEXT_PUBLIC_POSTHOG_API_KEY`: The API key for your PostHog project.
 - `NEXT_PUBLIC_POSTHOG_HOST`: The host for your PostHog project.
 
+- `OPENAI_API_KEY`: The API key for the OpenAI API.
+
 Create a `.env.local` file at the root of the project and add these variables to it.
 
 ## Installation