README: add notes on uniplot limitations

Author: marcom

README.md

@@ -63,7 +63,15 @@ PlotRNA.plot_structure_makie("(((...)))")
 
 ### Terminal plotting with UnicodePlots
 
-Plotting in the terminal is supported via UnicodePlots.
+Plotting in the terminal is supported via UnicodePlots with
+coordinates generated by ViennaRNA.
+
+Note: this is still considered experimental.  There are still some
+problems with plot sizes and aspect ratios. Additionally, when calling
+`uniplot` with an illegal structure or unbalanced parentheses it is
+possible to produce a segfault (coming from `plot_coords` in ViennaRNA
+that is used to generate coordinates for plotting).  See:
+[https://github.com/marcom/ViennaRNA.jl/issues/13](https://github.com/marcom/ViennaRNA.jl/issues/13).
 
 ```julia
 using UnicodePlots, PlotRNA