Update TeamsFx-preview-and-customize-app-manifest.md

msteams-platform/toolkit/TeamsFx-preview-and-customize-app-manifest.md

@@ -59,15 +59,14 @@ For example, you can put your manifest.json file in `test/test.json`, and update
 1. You can define your own environment variables. The default manifest.json contains some placeholders with format of ${{xx_xx}}. You can define your own environment variables and add placeholders in the manifest.json file.
 For example, you can customize app description by defining a new environment variable in env/.env.xx file, and update manifest.json with corresponding placeholder.
 
-`.env.dev`
+ `.env.dev`
 
-```text
- TEAMS_APP_DESCRIPTION=This is an amazing app
-```
+ ```text
+ TEAMS_APP_DESCRIPTION=This is an amazing app
+ ```
+ `manifest.json`
 
-`manifest.json`
-
-```json
+ ```json
  {
  "$schema": "https://developer.microsoft.com/en-us/json-schemas/teams/v1.16/MicrosoftTeams.schema.json",
  "manifestVersion": "1.16",
@@ -76,7 +75,52 @@ For example, you can customize app description by defining a new environment var
  "full": "Full description of tab0418"
  },
  }
-```
+ ```
+
+1. Starting with Teams Toolkit 5.10, using the `file` function you can store the value of a field, such as a lengthy or multiline app description, in a separate text file. For example, create a `description.txt` file in the parent folder of `manifest.json` to store your app's complete description. Then, set the value of `description.full` in `manifest.json` as `$[file('description.txt')]`. Teams Toolkit will read the content from the text file and use it as full description when building an app package.
+
+ `description.txt`
+
+ ```text
+ This is the full description.
+ ```
+
+ `manifest.json`
+
+ ```json
+ {
+ "$schema": "https://developer.microsoft.com/en-us/json-schemas/teams/v1.16/MicrosoftTeams.schema.json",
+ "manifestVersion": "1.16",
+ "description": {
+ "short": "Short description of tab",
+ "full": "$[file('./description.txt')]"
+ },
+ }
+ ```
+
+ You could either put the file path in env/.env.xx and update the input parameter function of file function to placeholder in ${{xx_xx}} format.
+
+
+ `.env.dev`
+
+ ```text
+ DESCRIPTION_PATH=./description.txt
+ ```
+
+ `manifest.json`
+
+ ```json
+ {
+ "$schema": "https://developer.microsoft.com/en-us/json-schemas/teams/v1.16/MicrosoftTeams.schema.json",
+ "manifestVersion": "1.16",
+ "description": {
+ "short": "Short description of tab",
+ "full": "$[file(${{DESCRIPTION_PATH}})]"
+ },
+ }
+ ```
+
+
 
 ## Validate your app