Master's Thesis Adviser Co-Authorship?
From a formal point of view co-authorship should involve a certain definable contribution. The Vancouver Protocol makes the following definition (here in the form presented by the BMJ: 


  Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; AND Drafting the work or revising it critically for important intellectual content; AND Final approval of the version to be published; AND Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.


You state that your advisor did not contribute much to the research questions or methodology. I further do not know your background so I can only judge from your question and provide general comments on your question. Writing up your research from a thesis to a publishable manuscript is a skill which is normally learned through graduate school. I am therefore thinking that you may still need quite a bit of guidance to manage the transition of your thesis material to the manuscript format. If your advisor is willing to help you with this part and the scientific input required to do so then co-authorship may well be warranted. So the co-authorship question should be answered on the final product and the contributions that went into it, and not necessarily what went into just your thesis.