docs: Move docs into docs/

docs/highlighters/brackets.md

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+zsh-syntax-highlighting / highlighters / brackets
+-------------------------------------------------
+
+This is the `brackets` highlighter, that highlights brackets and parentheses, and
+matches them.
+
+
+### How to tweak it
+
+This highlighter defines the following styles:
+
+* `bracket-error` - unmatched brackets
+* `bracket-level-N` - brackets with nest level N
+* `cursor-matchingbracket` - the matching bracket, if cursor is on a bracket
+
+To override one of those styles, change its entry in `ZSH_HIGHLIGHT_STYLES`,
+for example in `~/.zshrc`:
+
+    # To define styles for nested brackets up to level 4
+    ZSH_HIGHLIGHT_STYLES[bracket-level-1]='fg=blue,bold'
+    ZSH_HIGHLIGHT_STYLES[bracket-level-2]='fg=red,bold'
+    ZSH_HIGHLIGHT_STYLES[bracket-level-3]='fg=yellow,bold'
+    ZSH_HIGHLIGHT_STYLES[bracket-level-4]='fg=magenta,bold'
+
+The syntax for declaring styles is documented in [the `zshzle(1)` manual
+page](http://zsh.sourceforge.net/Doc/Release/Zsh-Line-Editor.html#SEC135).