Update README

Author: ramon-astudillo

README.md

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 Transition-based AMR Parser
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-Neural transition-based parser for Abstract Meaning Representation (AMR) producing state-of-the-art AMR parsing and reliable token to node alignments. See below for the different versions and corresponding papers
+Neural transition-based parser for Abstract Meaning Representation (AMR) producing state-of-the-art AMR parsing and reliable token to node alignments. See below for the different versions and corresponding papers. Note that, as of now, Structured-BART does not support standalone parsing mode. Use the `action-pointer` branch to get a parser that can work standalone.
 
 ### Structured-BART