[TASK] Improve log location explanation (#1013)

* [TASK] Improve log location explanation

* [TASK] Streamline placeholders in explanation

* [TASK] Add a missing file annotation

Resolves: #737
Co-authored-by: Mathias Brodala <mbrodala@pagemachine.de>

Documentation/ApiOverview/Logging/Configuration/Index.rst

@@ -53,12 +53,12 @@ The above configuration applies to **all** log entries of level "ERROR" or above
 
 .. important::
 
-    Since TYPO3 v9 the default folder for log files is `typo3temp/var/log`. In v8 it was `typo3temp/var/logs`
-    and older versions used `typo3temp/logs`.
-
-.. important::
-
-    Since TYPO3 v9 it is possible (and a good practice) to store temporary files (`typo3temp/var`) outside the document root).
+    Since TYPO3 v9 the default folder for log files is :file:`<var-path>/log`.
+    The `<var-path>` in a non-Composer installation (Classic Mode) is :file:`typo3temp/var/`,
+    in a Composer based installation it is :file:`<project-root>/var/` instead, unless configured otherwise.
+    See class :php:`\TYPO3\CMS\Core\Core\Environment` for defaults in both cases.
+    Since TYPO3 v9 it is possible (and a good practice) to store temporary files
+    outside the document root.
 
 To apply a special configuration for the controllers of the *examples* extension,
 use the following configuration: