docs: Add documentation for `text_rendering_mode` (#46358)

Kunall Banerjee created 

We added support for it in
https://github.com/zed-industries/zed/pull/45423. It’s already in
preview, but not yet in stable. So I’m going to keep this in my drafts
till then.

Release Notes:

- N/A

Change summary

docs/src/configuring-zed.md | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)

Detailed changes

docs/src/configuring-zed.md 🔗 

@@ -4317,6 +4317,38 @@ Example command to set the title: `echo -e "\e]2;New Title\007";`
 },
 ```
 
+## Text Rendering Mode
+
+- Description: The text rendering mode to use.
+- Setting: `text_rendering_mode`
+- Default: `platform_default`
+
+**Options**
+
+1. Use grayscale text rendering.
+
+```json [settings]
+{
+  "text_rendering_mode": "grayscale"
+}
+```
+
+2. Use subpixel (ClearType-style) text rendering.
+
+```json [settings]
+{
+  "text_rendering_mode": "subpixel"
+}
+```
+
+3. Use platform default behavior.
+
+```json [settings]
+{
+  "text_rendering_mode": "platform_default"
+}
+```
+
 ## Theme
 
 - Description: The theme setting can be specified in two forms - either as the name of a theme or as an object containing the `mode`, `dark`, and `light` themes for the Zed UI.