bt87 added

src/nbody/evolve/aarseth/nbody0/README

@@ -23,10 +23,9 @@ improve readability.
 
 Later additions:
 
-(jan-2000) The fortran-C interfaces have been converted to F77_FUNC macros, for which
-           you need NEMO.
+(jan-2000) The fortran-C interfaces have been converted to F77_FUNC macros,
+           for which you need NEMO.
 (feb-2004) Added an option to do better timestep control (e.g. for figure8 orbit)
-
 (sep-2018) Loaded ftp://ftp.ast.cam.ac.uk/pub/sverre/nbody0/nbody0.f as nbody0_sja.f
            Described as "Compact fourth-order Hermite block-step code."
            See also https://www.ast.cam.ac.uk/~sverre/web/pages/nbody.htm
@@ -35,3 +34,5 @@ Later additions:
 	   cat nbody0_sja.f  | sed 's/50)/256)/g' > nbody0_256.f
 (jan-2025) Retrieved the original again as nbody0_sja.f - RIP Sverre.
            (same as nbody0h4.f except for maximum number of bodies)
+           The BT87 code is preserved as nbody0_bt87.f, exactly all 262 lines,
+	   but note Sverre never archived this version.