docs(README): breakpoint removal (#422)

Update help docs to indicate that breakpoints can also be removed

doc/nvim-dap-ui.txt

@@ -428,6 +428,7 @@ Lists all breakpoints currently set.
 Mappings:
 - `open`: Jump to the location the breakpoint is set
 - `toggle`: Enable/disable the selected breakpoint
+- `remove`: Remove breakpoint. Only works on enabled breakpoints.
 
 
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@@ -436,4 +437,4 @@ dapui.elements.console                                  *dapui.elements.console*
 The console window used by nvim-dap for the integrated terminal.
 
 
- vim:tw=78:ts=8:noet:ft=help:norl:
+ vim:tw=78:ts=8:noet:ft=help:norl: