docs: fix by proofreading

Co-authored-by: MGatner <[email protected]>

Author: kenjis

user_guide_src/source/installation/installing_manual.rst

@@ -29,7 +29,7 @@ and extract it to become your project root.
 Initial Configuration
 =====================
 
-After installation, a few initial configuration is required.
+After installation, a few initial configurations are required.
 See :ref:`initial-configuration` for the detail.
 
 .. _installing-manual-upgrading: