docs: add car-notifier example

examples/car-notifier/Dockerfile

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+FROM alpine:latest
+
+COPY car-notifier.gpt ./car-notifier.gpt
+
+RUN apk update && apk add curl postgresql16-client --no-cache && curl https://get.gptscript.ai/install.sh | sh && mkdir /.cache && chmod 777 /.cache
+
+CMD ["gptscript", "--cache=false", "car-notifier.gpt"]

examples/car-notifier/README.md

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+# Car Notifier
+
+This is an example tool that fetches information about recently posted Toyota 4Runners
+on Phoenix Craigslist and sends an email with information about them.
+
+This tool is meant to be run as a cron job, daily, and requires a PostgreSQL database.
+It uses SendGrid to send the email.
+
+## Design
+
+This tool does not rely on any code besides a Dockerfile and a GPTScript. The Dockerfile
+is only used to containerize the environment that the GPTScript will run in.
+
+## Run the Example
+
+Prerequisites:
+- A PostgreSQL database, and a connection URL to it
+- A SendGrid API key
+- `psql` CLI client for PostgreSQL
+- `curl`
+
+Before running the script (or building the Dockerfile), be sure to edit it and fill in
+every occurrence  of `<email address>` and `<name>`. Unfortunately, there is no
+straightforward way to provide this information through environment variables, due to
+issues with escaping quotes in the cURL command that the LLM will run.
+
+```bash
+# Set up the environment variables
+export PGURL=your-postgres-connection-url
+export SENDGRID_API_KEY=your-sendgrid-api-key
+
+# Run the script
+gptscript --cache=false car-notifier.gpt
+```

examples/car-notifier/car-notifier.gpt

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+tools: send_email, sys.http.html2text, sys.write, sys.exec?
+
+Visit https://phoenix.craigslist.org/search/cta?postedToday=1&query=4runner&sort=date to get information about the
+4Runners listed today.
+
+Check the PostgreSQL database and see if any of these vehicles have already been stored. If they have been, ignore them.
+The `psql` command is available. The database connection string is in the environment variable PGURL. The table is
+called "vehicles". If the table doesn't exist yet, create it. The only thing that needs to be stored in the table
+is the URL for each vehicle. Don't add any other fields.
+
+For each vehicle that was not already in the database, store the information about it into the database, and send
+an email with information about those vehicles. If there are no new vehicles, then don't send an email.
+
+---
+name: send_email
+description: sends an email with the provided contents
+args: contents: the contents of the email to send
+tools: sys.http.html2text, sys.exec?
+
+IMPORTANT: when setting --header or -H on a cURL command, always use double quotes, never single quotes!
+IMPORTANT: when setting --data or -d on a cURL command, always use single quotes, never double quotes! And always escape newlines! (They should look like "\\n")
+
+The SendGrid API key is in the environment variable SENDGRID_API_KEY.
+
+Perform the following actions in this order:
+1. View the contents of https://docs.sendgrid.com/for-developers/sending-email/api-getting-started to learn about the SendGrid API.
+2. Run a cURL command to send an email using the SendGrid API, with the following information:
+   to: <email address> (name: <name>)
+   from: <email address> (name: <name>)
+   reply to: <email address> (name: <name>)
+   subject: "4Runner Listings"
+   content: $contents