Trac #29477: Fix enumeration alignment in doc of RealField

Noticed after reading that [https://groups.google.com/d/msg/sage-devel
/CRBT-oFxn3c/NB1IUJgdBAAJ sage-devel thread].

URL: https://trac.sagemath.org/29477
Reported by: slabbe
Ticket author(s): Sébastien Labbé
Reviewer(s): Frédéric Chapoton

src/sage/rings/real_mpfr.pyx

@@ -398,7 +398,7 @@ cpdef RealField(int prec=53, int sci_not=0, rnd=MPFR_RNDN):
       - ``'RNDU'`` -- round towards plus infinity
       - ``'RNDA'`` -- round away from zero
       - ``'RNDF'`` -- faithful rounding (currently experimental; not
-                      guaranteed correct for every operation)
+        guaranteed correct for every operation)
       - for specialized applications, the rounding mode can also be
         given as an integer value of type ``mpfr_rnd_t``. However, the
         exact values are unspecified.