Keyboard shortcuts docs#2981 (#325)

* Add section for keyboard shortcuts docs

Author: ahmedibrahim404

docs/_sidebar.md

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     * [Online Forums](/chapter8/1onlineforums.md)
     * [FAQ](/chapter8/2cvfaq.md)
     * [Understanding Error Messages](/chapter8/3cverrormessages.md)
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+    * [Keyboard Shortcuts](/chapter8/4shortcuts.md)

docs/chapter8/4shortcuts.md

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+# Keyboard Shortcuts
+
+| Keys   |      Actions |
+|----------|:-------------:|
+| Copy |  Ctrl + c |
+| Cut | Ctrl + x |
+| Paste | Ctrl + v |
+| Undo | Ctrl + z |
+| Redo | Ctrl + y |
+| Delete Object(s) | Delete |
+| Select All | Ctrl + a |
+| De-select | ESC |
+| Deattach objects before placing | Backspace |
+| Multi-object Select | Ctrl + scoll using mouse |
+| Save Project Online | Ctrl + s |
+| Save Project Offline | Ctrl + Shift + s |
+| Open Project | Ctrl + o |
+| Download Image | Ctrl + d |
+| Zoom in | Ctrl + '+' |
+| Zoom out | Ctrl + '-' |
+| Enter Time in diagram | T |
+| Make object looks Right | Arrow Right |
+| Make object looks Left | Arrow Left |
+| Make object looks Up | Arrow Up |
+| Make object looks Down | Arrow Down |
+| Open Documentation Page | F1 |