doc: Initial MkDocs (material theme) setup for BIT manual

MkDocs setup using the material theme.
Thank you to Kosta Vukicevic (@stcksmsh) (#1659) providing a first prototyp.

Current content of the manual is not modified but nearly identical to the one generated by Sphinx setup.

.codespellrc

@@ -1,6 +1,6 @@
 [codespell]
 # Folders and files to skip
-skip = .codespellrc,*.po,Makefile,*.desktop,.git,__pycache__,*.pyc,languages.py,_build,TRANSLATIONS,./doc/manual/html
+skip = .codespellrc,*.po,Makefile,*.desktop,.git,__pycache__,*.pyc,languages.py,_build,TRANSLATIONS,./doc/manual/html,mkdocs.yml
 # Print N lines of surrounding context
 context = 1
 # Check hidden files also (empty means True)

.gitignore

@@ -45,6 +45,9 @@ qt/Makefile
 common/doc-dev/_build/doctrees
 common/doc-dev/_build/html
 
+# MkDocs
+doc/manual/html/
+
 # PyCharm IDE project settings
 .idea
 

README.md

@@ -8,8 +8,8 @@ Germar Reitze, Taylor Raack</sub><br />
 <sub>Copyright (C) 2022 Christian Buhtz, Michael Büker, Jürgen Altfeld</sub>
 
 _Back In Time_ is an easy-to-use tool to backup files and folders.
-It runs on GNU Linux (not on Windows or OS X/macOS) and provides a command line tool `backintime` and a
-GUI `backintime-qt` both written in Python3. It uses 
+It runs on GNU/Linux (not on Windows or OS X/macOS) and provides a command line
+tool `backintime` and a GUI `backintime-qt` both written in Python3. It uses 
 [`rsync`](https://rsync.samba.org/) to take manual or scheduled snapshots and
 stores them locally or remotely through SSH. Each snapshot is in its own folder
 with copies of the original files, but unchanged files are hard-linked between
@@ -34,11 +34,12 @@ those labeled as [good first issues](https://github.com/bit-team/backintime/labe
 and [help wanted](https://github.com/bit-team/backintime/issues?q=is%3Aissue+is%3Aopen+label%3AHELP-WANTED).
 
 ## The team
-The current team started in summer of 2022 (with #1232) and constitutes the
-project's 3rd generation of maintainers. Consisting of three members with
-diverse backgrounds (@aryoda, @buhtz, @emtiu), the team benefits from the
-assistance of the former maintainer, @Germar, who contributes from behind the
-scenes.
+The current team started in summer of 2022
+(with [#1232](https://github.com/bit-team/backintime/issues/1232)) and
+constitutes the project's 3rd generation of maintainers. Consisting of three
+members with diverse backgrounds (@aryoda, @buhtz, @emtiu), the team benefits
+from the assistance of the former maintainer, @Germar, who contributes from
+behind the scenes.
 
 All team members are engaged in every aspect of the project, including code
 analysis, documentation, solving issues, and the implementation of new

doc/README.md

@@ -0,0 +1,20 @@
+This directory contains the source files for various types of documentation
+for _Back In Time_.
+
+- `manual`: User Manual
+
+### How to reduce file size of images
+For PNG images `optipng` could be used. *Attention*: By default it overwrites
+the original files. The following command use the highest possible optimization
+and write the result in a subfolder.
+
+    $ optipng --dir subfolder -o7 *.png
+
+As an alternative `pngcrush` can be used. The following determine the best
+algorithm by its own.
+
+    $ pngcrush -d subfolder -brute *.png
+
+Applied to a set of _Back In Time_ dark mode screenshots, their file size
+was reduced by approximately 13%. Both applications show no significant
+differences. The visual result is indistinguishable from the original.

doc/manual/mkdocs.yml

@@ -0,0 +1,77 @@
+# Project information
+site_name: Back In Time - User Manual
+site_author: BIT Team
+
+# Source files (markdown)
+docs_dir: src
+# Output directory
+site_dir: html
+# site_url: https://backintime-docs.readthedocs.io/en/latest/
+# site_description: Back In Time is a simple backup tool for Linux inspired by "FlyBack".
+
+# Repository information
+repo_name: backintime
+# repo_url: https://github.com/bit-team/backintime
+
+# Entrie labels determined by the the 1st level heading
+nav: 
+  - 'index.md'
+  - 'quick-start.md'
+  - 'main-window.md'
+  - 'settings.md'
+  - 'snapshots-dialog.md'
+  - 'log.md'
+  - 'additional.md'
+
+markdown_extensions:
+  # Boxex for warnings, etc.
+  # https://squidfunk.github.io/mkdocs-material/reference/admonitions/
+  - admonition
+  - toc:
+      permalink: true  
+
+# Configuration
+theme:
+    name: material
+    logo: _images/logo48.png
+    favicon: _images/logo48.png
+    language: en
+    features:
+      # Load content of main page only instead of the whole site
+      - navigation.instant
+      # Loading in background while hovering over the navigation item
+      - navigation.instant.prefetch
+      # Unfold all entries in navigation side bar
+      - navigation.expand
+      # Render navigation path on above the title of each page
+      - navigation.path
+      # Back-to-top-button
+      - navigation.top
+      # Render sub-headings in navigation side bar
+      - toc.integrate
+      - toc.follow
+      # Highlight search results
+      - search.highlight
+      # Link current document to GitHub
+      - content.action.edit
+      - content.action.view
+      # Copy and highlight code blocks
+      - content.code.copy
+      - content.code.select
+    # Colorsettings regarding dark/light mode
+    palette:
+    - media: "(prefers-color-scheme: light)"
+      scheme: default
+      primary: blue grey
+      accent: blue
+      toggle:
+        icon: material/toggle-switch
+        name: Switch to dark mode
+    - media: "(prefers-color-scheme: dark)"
+      scheme: slate
+      primary: grey
+      accent: blue
+      toggle:
+        icon: material/toggle-switch-off
+        name: Switch to system preference
+