Add Linux manuals refs to bibliography database

Author: shorodilov

src/linux/index.txt

@@ -3,17 +3,14 @@
     :author: Serhii Horodilov
     :keywords: linux, basics, index
 
-.. todo
-
-.. attention:: Page is under construction
-
-    .. figure:: /../assets/img/construction.svg
-        :figwidth: 250
-        :align: center
-
 ###############################################################################
                              Linux Basics
 ###############################################################################
 
+Linux is a powerful, open-source operating system widely used in various
+domains, from embedded systems to supercomputers. It is known for its
+stability, security, and flexibility, making it a preferred choice for
+developers, especially in server environments.
+
 .. toctree::
     :name: linux

src/refs.bib

@@ -225,3 +225,19 @@ @misc{medium:db-acid-cap
     date = {2017.1.12},
     url = {https://cinish.medium.com/database-acid-cap-isolation-levels-371b7e06a112}
 }
+
+@manual{linux-intro,
+    title = {Introduction to Linux. A hands on guide},
+    author = {Machtelt Garrels},
+}
+
+@manual{linux-tutorial,
+    title = {Linux Tutorial},
+    author = {Jon Wakelin and Liam Gretton and Gary Gilchrist and Teri Forey},
+}
+
+@manual{linux-grd1-manual,
+    title = {Introduction to Linux for Users and Administrators},
+    author = {Tobias Elsner and Anselm Lingnau},
+    editor = {Anselm Lingnau},
+}