Clarify the "env" launch configuration setting.

[clayborg]

Summary

A few users recently were trying to set environment values when using lldb-vscode and were unsure of the format of the "env" launch configuration setting. Clarify the exact format as when users add the "env" launch config setting, they can see this help string in the IDE.

[wallace]

thank you!

lldb/tools/lldb-vscode/package.json

"debuggers": [
               },
               "cwd": {
                 "type": "string",
                 "description": "Program working directory.",
                 "default": "${workspaceRoot}"
               },
               "env": {
                 "type": "array",
-                "description": "Additional environment variables.",
+                "description": "Additional environment variables to set when launching the program. This is an array of strings that contains the variable name followed by an optional '=' character and the environment variable's value. Example:  [\"FOO=BAR\", \"BAZ\"]",
                 "default": []
               },
               "stopOnEntry": {
                 "type": "boolean",
                 "description": "Automatically stop after launch.",
                 "default": false
               },
               "disableASLR": {