Update server-installation.mdx for inactiveTimeoutMinutes in app.conf

docs/basic/server-installation.mdx

@@ -140,6 +140,7 @@ logPostOnly = true
 origin = "https://door.casdoor.com"
 staticBaseUrl = "https://cdn.casbin.org"
 enableGzip = true
+inactiveTimeoutMinutes =
 ```
 
 - `appname` is the application name, which currently has no practical use.
@@ -163,6 +164,7 @@ As a beginner, you only need to modify two items: `driverName` and `dataSourceNa
 - `origin` is the origin backend domain name.
 - `staticBaseUrl` is the address of the static image used when the system initializes the database.
 - `enableGzip` will accept and respond with gzip encoding if the request header includes `Accept-Encoding=gzip`.
+- `inactiveTimeoutMinutes` sets the maximum number of minutes of inactivity. If the inactivity time reaches this value, then casdoor will log the user out. Empty value or value less than or equal to 0 means there is no limit on the user's inactivity time.
 
 ### Via Environment Variables