document new symbol overwrite feature

Author: Stephan Dilly

KEY_CONFIG.md

@@ -15,3 +15,19 @@ The location of the file depends on your OS:
 * `%APPDATA%/gitui/key_config.ron` (Windows)
 
 Here is a [vim style key config](vim_style_key_config.ron) with `h`, `j`, `k`, `l` to navigate. Use it to copy the content into `key_config.ron` to get vim style key bindings.
+
+# Key Symbols
+
+Similar to the above GitUI allows you to change the way the UI visualizes key combos containing special keys like `enter`(default: `⏎`) and `shift`(default: `⇧`).
+
+If we can find a file `key_symbols.ron` in the above folders we apply the overwrites in it.
+
+Example content of this file looks like:
+
+```
+(
+    enter: Some("enter"),
+    shift: Some("shift-")
+)
+```
+This example will only overwrite two symbols. Find all possible symbols to overwrite in `symbols.rs` in the type `KeySymbolsFile` ([src/keys/symbols.rs](https://github.com/extrawurst/gitui/blob/master/src/keys/symbols.rs))