chore(docs): Update default proxy URL in CLI docs (#1271)

Someone [reported some
confusion](https://discord.com/channels/933657521581858818/933657523049885698/1240288588906762350)
with respect to the documented default proxy URL - this fix makes it
slightly more verbose but hopefully removes any ambiguity.

Technically all parts of the proxy uri are set by environment variables,
but the database name in particular is the only one that has a "dynamic"
default set by the project name - not sure if it's worth expanding the
CLI description to mention that the proxy URL really defaults to:
```
postgresql://{ELECTRIC_DATABASE_USER}:{ELECTRIC_DATABASE_PASSWORD}@{ELECTRIC_DATABASE_HOST}:{ELECTRIC_DATABASE_PORT}/{ELECTRIC_DATABASE_NAME}
```
feels like it would be _too_ verbose.

docs/api/cli.md

@@ -50,7 +50,7 @@ All arguments are optional. The principal ones are described below:
 | Argument or Env var  | Value        | Description                              |
 |----------------------|--------------|------------------------------------------|
 | <span className="no-wrap">`--service`</span><br/><span className="no-wrap">`-s`</span><br/>`ELECTRIC_SERVICE` |`<url>` | Provides the url to connect to the [Electric sync service](./service.md).<br /> Defaults to `http://localhost:5133`. |
-| <span className="no-wrap">`--proxy`</span><br/><span className="no-wrap">`-p`</span><br/>`ELECTRIC_PROXY` | `<url>` | Provides the url to connect to Electric's database proxy.<br /> Defaults to <span class="break-all">`postgresql://postgres:proxy_password@localhost:65432/electric`</span>. |
+| <span className="no-wrap">`--proxy`</span><br/><span className="no-wrap">`-p`</span><br/>`ELECTRIC_PROXY` | `<url>` | Provides the url to connect to Electric's database proxy.<br /> Defaults to <span class="break-all">`postgresql://postgres:proxy_password@localhost:65432/your_db_name`</span>, where `your_db_name` is the name provided through [`ELECTRIC_DATABASE_NAME`](#electric_database_name). |
 | <span className="no-wrap">`--client-path`</span><br /><span className="no-wrap">`-o`</span><br />`ELECTRIC_CLIENT_PATH` | `<path>` | Specifies the output location for the generated client.<br /> Defaults to `./src/generated/client` |
 | <span className="no-wrap">`--watch`</span><br /><span className="no-wrap">`-w`</span> | `<pollingInterval>` | Run the generator in watch mode. Accepts an optional polling interval (in milliseconds) which defines how often to poll Electric for database migrations.<br /> The default polling interval is 1000ms. |
 | <span className="no-wrap">`--with-migrations`</span> | `<command>` | Specify a command to run migrations against an ephemeral postgres in order to create a client. [See details below](#local-only-first-mode) |