docs: Add section about terminal contrast adjustments (#35369)

Closes #35146

This change adds documentation for the `terminal.minimum_contrast`
setting to the docs as we've had a lot of reports regarding the contrast
adjustments, yet are missing proper documentation (aside from that in
the `defaults.json`) for it.

Release Notes:

- N/A

docs/src/configuring-zed.md

@@ -2588,6 +2588,7 @@ List of `integer` column numbers
     "font_features": null,
     "font_size": null,
     "line_height": "comfortable",
+    "minimum_contrast": 45,
     "option_as_meta": false,
     "button": true,
     "shell": "system",
@@ -2883,6 +2884,30 @@ See Buffer Font Features
 }
 ```
 
+### Terminal: Minimum Contrast
+
+- Description: Controls the minimum contrast between foreground and background colors in the terminal. Uses the APCA (Accessible Perceptual Contrast Algorithm) for color adjustments. Set this to 0 to disable this feature.
+- Setting: `minimum_contrast`
+- Default: `45`
+
+**Options**
+
+`integer` values from 0 to 106. Common recommended values:
+
+- `0`: No contrast adjustment
+- `45`: Minimum for large fluent text (default)
+- `60`: Minimum for other content text
+- `75`: Minimum for body text
+- `90`: Preferred for body text
+
+```json
+{
+  "terminal": {
+    "minimum_contrast": 45
+  }
+}
+```
+
 ### Terminal: Option As Meta
 
 - Description: Re-interprets the option keys to act like a 'meta' key, like in Emacs.