Add: some useful keys in Vim mode

trees/uts-002F.tree

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+\import{macros}
+% clifford hopf spin tt ag math draft tech exp notes
+\tag{tech}
+\tag{notes}
+\tag{draft}
+
+\mdnote{some useful keys in Vim mode}{
+I'm a bit rusty on Vim mode, here are some useful keys that I like using:
+
+- save & quit
+    - should stick to `cmd+s` for saving, `cmd+w` for closing a tab
+    - `ZZ` to save and quit
+    - `:q!` to quit without saving
+- move
+    - `gg` for beginning, `G` for end
+    - `w`/`b` to move forward/backward by word
+    - shift+`w`/`b` to move by space-separated words
+    - left `hj` are for left, down; right `kl` are for right, up
+        - I can never remember this in my muscle memory
+    - `0` to move to the beginning of the line
+        - I don't like `^` and `$` because they are difficult to reach
+- move & edit
+    - `i` to enter INSERT mode
+    - `A` to append at the end of the line
+    - `0i` to insert at the beginning of the line
+    - `R` to replace
+    - `u` to undo, surprisingly `Ctrl`+`r` to redo
+    - `x`/`dw`/`dd` to delete a character/word/line
+    - `yyp` to duplicate a line
+- add a number before a command to repeat it, e.g. `3j`, `3W`, `3u` for the impatient
+- search
+    - `/` to search forward, `n`/`p` to go to next/previous match
+    - `?` to search backward
+    -  remember to press `Enter` after typing the search term
+}