Update file-based program doc (#48943)

Author: jjonescz

documentation/general/dotnet-run-file.md

@@ -7,6 +7,8 @@ We call these *file-based programs* (as opposed to *project-based programs*).
 dotnet run file.cs
 ```
 
+See also [IDE spec](https://github.com/dotnet/roslyn/blob/main/docs/features/file-based-programs-vscode.md).
+
 ## Motivation
 
 File-based programs
@@ -71,7 +73,7 @@ Internally, the SDK CLI detects entry points by parsing all `.cs` files in the d
 and checking which ones contain top-level statements (`Main` methods are not supported for now as that would require full semantic analysis, not just parsing).
 Results of this detection are used to exclude other entry points from [builds](#multiple-entry-points) and [app directive collection](#directives-for-project-metadata).
 This means the CLI might consider a file to be an entry point which later the compiler doesn't
-(for example because its top-level statements are under `#if SYMBOL` and the build has `DefineConstants=SYMBOL`).
+(for example because its top-level statements are under `#if !SYMBOL` and the build has `DefineConstants=SYMBOL`).
 However such inconsistencies should be rare and hence that is a better trade off than letting the compiler decide which files are entry points
 because that could require multiple builds (first determine entry points and then re-build with app directives except those from other entry points).
 To avoid parsing all C# files twice (in CLI and in the compiler), the CLI could use the compiler server for parsing so the trees are reused