add showcase in doc and removing screenshot out from main readme

doc/showcases.md

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+# Screenshots and videos of the app in action
+
+
+## Golang struct type
+
+Struct type references in multiple Go 󰟓  files
+
+![go_reference](https://user-images.githubusercontent.com/1681295/119123823-54b3b180-ba73-11eb-8790-097601e10f6a.gif)
+
+This feature can provide you info in which function/class/method the variable was referenced. It is handy for a large
+project where class/function definition is too long to fit into the preview window. Also provides a bird's eye view of where the
+variable is:
+
+- Referenced
+- Modified
+- Defined
+- Called
+
+
+### Definition preview
+
+Using treesitter and LSP to view the symbol definition
+
+![image](https://user-images.githubusercontent.com/1681295/139771978-bbc970a5-be9f-42cf-8942-3477485bd89c.png)
+
+### Sidebar, folding, outline
+
+Treesitter outline and Diagnostics
+<img width="708" alt="image" src="https://user-images.githubusercontent.com/1681295/174791609-0023e68f-f1f4-4335-9ea2-d2360e9f0bfd.png">
+<img width="733" alt="image" src="https://user-images.githubusercontent.com/1681295/174804579-26f87fbf-426b-46d0-a7a3-a5aab69c032f.png">
+
+The side panel is vim buffer. You can toggle folds with za/zo/zc
+
+
+Calltree (Expandable LSP call hierarchy)
+<img width="769" alt="image" src="https://user-images.githubusercontent.com/1681295/176998572-e39fc968-4c8c-475d-b3b8-fb7991663646.png">
+
+### GUI and multigrid support
+
+You can load a different font size for floating win
+
+![multigrid2](https://user-images.githubusercontent.com/1681295/139196378-bf69ade9-c916-42a9-a91f-cccb39b9c4eb.jpg)
+
+### Document Symbol and navigate through the list
+
+![doc_symbol_and_navigate](https://user-images.githubusercontent.com/1681295/148642747-1870b1a4-67c2-4a0d-8a41-d462ecdc663e.gif)
+The key binding to navigate in the list.
+
+- up and down key
+- `<Ctrl-f/b>` for page up and down
+- number key 1~9 go to the ith item.
+- If there are loads of results, would be good to use fzy search prompt to filter out the result you are interested.
+
+### Workspace Symbol
+
+![workspace symbol](https://github.com/ray-x/files/blob/master/img/navigator/workspace_symbol.gif?raw=true)
+
+### highlight document symbol and jump between reference
+
+![multiple_symbol_hi3](https://user-images.githubusercontent.com/1681295/120067627-f9f80680-c0bf-11eb-9216-18e5c8547f59.gif)
+
+## Current symbol highlight and jump backward/forward between symbols
+
+Document highlight provided by LSP.
+Jump between symbols with treesitter (with `]r` and `[r`)
+![doc jump](https://github.com/ray-x/files/blob/master/img/navigator/doc_hl_jump.gif?raw=true)
+
+### Diagnostic
+
+Visual studio code style show errors minimap in scroll bar area
+(Check setup for `diagnostic_scrollbar_sign`)
+
+![diagnostic_scroll_bar](https://user-images.githubusercontent.com/1681295/128736430-e365523d-810c-4c16-a3b4-c74969f45f0b.jpg)
+
+Diagnostic in single bufer
+
+![diagnostic](https://github.com/ray-x/files/blob/master/img/navigator/diag.jpg?raw=true)
+
+Show diagnostic in all buffers
+
+![diagnostic multi files](https://github.com/ray-x/files/blob/master/img/navigator/diagnostic_multiplefiles.jpg?raw=true)
+
+### Edit in preview window
+
+You can in place edit your code in floating window
+
+<https://user-images.githubusercontent.com/1681295/121832919-89cbc080-cd0e-11eb-9778-11d0f356b38d.mov>
+
+(Note: This feature only available in `find reference` and `find diagnostic`, You can not add/remove lines in floating window)
+
+### Implementation
+
+![implementation](https://user-images.githubusercontent.com/1681295/118735346-967e0580-b883-11eb-8c1e-88c5810f7e05.jpg?raw=true)
+
+### Fzy search in reference
+
+![fzy_reference](https://github.com/ray-x/files/blob/master/img/navigator/fzy_reference.jpg?raw=true)
+
+### Code actions
+
+![code actions](https://github.com/ray-x/files/blob/master/img/navigator/codeaction.jpg?raw=true)
+
+### Symbol rename
+
+<https://user-images.githubusercontent.com/1681295/200327179-0fc84660-44a8-4ee1-9631-2cc7a17b0b12.mov>
+
+#### Fill struct with gopls
+
+![code actions fill struct](https://github.com/ray-x/files/blob/master/img/navigator/fill_struct.gif?raw=true)
+
+### Code preview with highlight
+
+![treesitter_preview](https://user-images.githubusercontent.com/1681295/118900852-4bccbe00-b955-11eb-82f6-0747b1b64e7c.jpg)
+
+### Treesitter symbol
+
+Treetsitter symbols in all buffers
+![treesitter](https://user-images.githubusercontent.com/1681295/118734953-cc6eba00-b882-11eb-9db8-0a052630d57e.jpg?raw=true)
+
+### Call hierarchy (incoming/outgoing calls)
+
+![incomming_calls](https://user-images.githubusercontent.com/1681295/142348079-49b71486-4f16-4f10-95c9-483aad11c262.jpg)
+
+### Light bulb if codeAction available
+
+![lightbulb](https://github.com/ray-x/files/blob/master/img/navigator/lightbulb.jpg?raw=true)
+
+### Codelens
+
+Codelens for gopls/golang. Garbage collection analyse:
+
+![codelens](https://user-images.githubusercontent.com/1681295/132428956-7835bf30-2ed5-4871-b2d7-7fbad22f63e8.jpg)
+
+Codelens for C++/ccls. Symbol reference
+
+![codelens_cpp_ccls](https://user-images.githubusercontent.com/1681295/132429134-abc6547e-79cc-44a4-b7a9-23550b895e51.jpg)
+
+### Predefined LSP symbol nerdfont/emoji
+
+![nerdfont](https://github.com/ray-x/files/blob/master/img/navigator/icon_nerd.jpg?raw=true)
+
+### Signature help
+
+Improved signature help with current parameter highlighted
+
+![signature](https://github.com/ray-x/files/blob/master/img/navigator/signature_with_highlight.jpg?raw=true)
+
+![show_signature](https://github.com/ray-x/files/blob/master/img/navigator/show_signnature.gif?raw=true "show_signature")
+