gh-38997:     Document RealIntervalField default printing configuration
    
As in the title.

Side note, is this actually a good idea? Maybe it was intended to be not
modifiable…

But modifying it has a practical advantage, sometimes you cannot control
these two option otherwise e.g. if you have a list of elements you may
need to extract each element and call `.str(...)` on it.

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- [x] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

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URL: #38997
Reported by: user202729
Reviewer(s): Travis Scrimshaw

Author: Release Manager

src/sage/rings/real_mpfi.pyx

@@ -120,6 +120,26 @@ satisfying, but we have chosen the latter.
     sage: a == 2
     False
 
+Some default printing options can be set by modifying module globals::
+
+    sage: from sage.rings import real_mpfi
+    sage: x = RIF(sqrt(2), sqrt(2)+1e-10); x
+    1.4142135624?
+    sage: real_mpfi.printing_error_digits = 2
+    sage: x
+    1.414213562424?51
+    sage: real_mpfi.printing_style = 'brackets'
+    sage: x
+    [1.4142135623730949 .. 1.4142135624730952]
+    sage: real_mpfi.printing_style = 'question'; real_mpfi.printing_error_digits = 0  # revert to default
+
+The default value of using scientific notation can be configured at field construction instead::
+
+    sage: RealIntervalField(53, sci_not=False)(0.5)
+    0.50000000000000000?
+    sage: RealIntervalField(53, sci_not=True)(0.5)
+    5.0000000000000000?e-1
+
 COMPARISONS:
 
 Comparison operations (``==``, ``!=``, ``<``, ``<=``, ``>``, ``>=``)