docs: add documentation for model aliases configuration

aider/website/docs/config/model_aliases.md

@@ -0,0 +1,57 @@
+# Model Aliases
+
+Model aliases allow you to create shorthand names for models you frequently use. This is particularly useful for models with long names or when you want to standardize model usage across your team.
+
+## Command Line Usage
+
+You can define aliases when launching aider using the `--alias` option:
+
+```bash
+aider --alias "fast:gpt-3.5-turbo" --alias "smart:gpt-4"
+```
+
+Multiple aliases can be defined by using the `--alias` option multiple times. Each alias definition should be in the format `alias:model-name`.
+
+## Configuration File
+
+You can also define aliases in your `.aider.conf.yml` file:
+
+```yaml
+alias:
+  - "fast:gpt-3.5-turbo"
+  - "smart:gpt-4"
+  - "code:claude-3-sonnet-20240229"
+```
+
+## Using Aliases
+
+Once defined, you can use the alias instead of the full model name:
+
+```bash
+aider --model fast  # Uses gpt-3.5-turbo
+aider --model smart  # Uses gpt-4
+```
+
+## Built-in Aliases
+
+Aider includes some built-in aliases for convenience:
+
+- `4`: gpt-4-0613
+- `4o`: gpt-4o-2024-08-06
+- `4-turbo`: gpt-4-1106-preview
+- `35turbo` or `35-turbo`: gpt-3.5-turbo
+- `3`: gpt-3.5-turbo
+- `sonnet`: claude-3-sonnet-20241022
+- `haiku`: claude-3-haiku-20241022
+- `opus`: claude-3-opus-20240229
+- `deepseek`: deepseek/deepseek-coder
+
+## Priority
+
+If the same alias is defined in multiple places, the priority is:
+
+1. Command line aliases (highest priority)
+2. Configuration file aliases
+3. Built-in aliases (lowest priority)
+
+This allows you to override built-in aliases with your own preferences.