Document default tsBuildInfoFile defaults (#2733)

Co-authored-by: Caleb ツ Everett <[email protected]>
Co-authored-by: Jake Bailey <[email protected]>

Author: everett1992

packages/tsconfig-reference/copy/en/options/tsBuildInfoFile.md

@@ -6,5 +6,12 @@ oneline: "The file to store `.tsbuildinfo` incremental build information in."
 This setting lets you specify a file for storing incremental compilation information as a part of composite projects which enables faster
 building of larger TypeScript codebases. You can read more about composite projects [in the handbook](/docs/handbook/project-references.html).
 
-By default it is in the same folder as your emitted JavaScript and has a `.tsbuildinfo` file extension.
-The default file name is based on the `outFile` option or your tsconfig file name.
+The default depends on a combination of other settings:
+
+- If `outFile` is set, the default is `<outFile>.tsbuildinfo`.
+- If `rootDir` and `outDir` are set, then the file is `<outDir>/<relative path to config from rootDir>/<config name>.tsbuildinfo`
+  For example, if `rootDir` is `src`, `outDir` is `dest`, and the config is
+  `./tsconfig.json`, then the default is `./tsconfig.tsbuildinfo`
+  as the relative path from `src/` to `./tsconfig.json` is `../`.
+- If `outDir` is set, then the default is `<outDir>/<config name>.tsbuildInfo`
+- Otherwise, the default is `<config name>.tsbuildInfo`