[readthedocs] Description for Occlum log config option

docs/readthedocs/docs/source/how_to_debug.md

@@ -5,3 +5,5 @@ To debug an app running upon Occlum, one can harness Occlum's builtin support fo
 Meanwhile, one can use `occlum mount` command to access and manipulate the secure filesystem for debug purpose.
 
 If the cause of a problem does not seem to be the app but Occlum itself, then one can take a glimpse into the inner workings of Occlum by checking out its log. Occlum's log level can be adjusted through `OCCLUM_LOG_LEVEL` environment variable. It has six levels: `off`, `error`, `warn`, `debug`, `info`, and `trace`. The default value is `off`, i.e., showing no log messages at all. The most verbose level is `trace`.
+
+The Occlum log output could be disabled totally for better security by setting `metadata.disable_log=true` in `Occlum.json` before building the Occlum instance. For detail please refer [Occlum Configuration](https://occlum.readthedocs.io/en/latest/occlum_configuration.html).

docs/readthedocs/docs/source/occlum_configuration.md

@@ -61,7 +61,14 @@ The template of `Occlum.json` is shown below.
         "version_number": 0,
         // Whether the enclave is debuggable through special SGX instructions.
         // For production enclave, it is IMPORTANT to set this value to false.
-        "debuggable": true
+        "debuggable": true,
+        // Whether the enclave is allowable to print Occlum log.
+        // Optional, if not set, in default it is false for debuggable enclave
+        // but true for production/release enclave for better security.
+        // Production/release enclave could explicitly set it false to have log
+        // output for debugging purpose. In this case, error log level is the
+        // only allowed log level.
+        "disable_log": false,
     },
     // Features
     "feature": {