NSBH-HM-docs.md

+# Notes
+
+* I think m1<m2 should be an error, because it's not safe to swap m1 and m2 without also swapping lambda1 and lambda2 (the user should know that they are not consistently handling the asymmetry between BHs and NSs). If we *do* include a check and do the swap, we should only swap lambda1 and lambda2 internally, and rely on SEOBNRv4HMROM to swap m1 and m2, because this introduces an extra sign in the odd modes which is done in an internal function.
+
+* I think we should do error checking both in lalsiminspiral and waveform cache, AND in the xlal functions, to be safe.
+
 # Changes to other lal modules
 - TunedTides: Added HM flag
 - LALSim.h: Added HM flag