feat(ui): add envvar popup with warnings (#54)

* feat: add support for input popup of envvar

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>

* chore: update README and ignore certain filetypes for popup

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>

* fix: readme doesn't support nested callout

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>

---------

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>

lua/avante/diff.lua

@@ -331,9 +331,10 @@ local function register_cursor_move_events(bufnr)
     end
 
     local hint = string.format(
-      " [Press <%s> for OURS, <%s> for THEIRS, <%s> for PREV, <%s> for NEXT] ",
+      " [Press <%s> for OURS, <%s> for THEIRS, <%s> for BOTH, <%s> for PREV, <%s> for NEXT] ",
       Config.diff.mappings.ours,
       Config.diff.mappings.theirs,
+      Config.diff.mappings.both,
       Config.diff.mappings.prev,
       Config.diff.mappings.next
     )