Improve minos cl docstring (#1085)

Closes #1072

Author: HDembinski

src/iminuit/minuit.py

@@ -1501,14 +1501,17 @@ def minos(
             Names of parameters to generate Minos errors for. If no positional
             arguments are given, Minos is run for each parameter.
         cl : float or None, optional
-            Confidence level of the interval. If not set or None, a standard 68 %
-            interval is computed (default). If 0 < cl < 1, the value is interpreted as
-            the confidence level (a probability). For convenience, values cl >= 1 are
-            interpreted as the probability content of a central symmetric interval
-            covering that many standard deviations of a normal distribution. For
-            example, cl=1 is interpreted as 68.3 %, and cl=2 is 84.3 %, and so on. Using
-            values other than 0.68, 0.9, 0.95, 0.99, 1, 2, 3, 4, 5 require the scipy
-            module.
+            Confidence level of the interval. If not set or None, a standard
+            interval is computed (default). A standard interval has about 68.3 %
+            confidence, which is the probability of being within one standard
+            deviation around the mean of a normal distribution. If 0 < cl < 1,
+            the value is interpreted as the confidence level (a probability).
+            For convenience, values cl >= 1 are interpreted as the probability
+            content of a central symmetric interval covering that many standard
+            deviations of a normal distribution. For example, cl=1 is
+            interpreted as about 68.3 %, and cl=2 as 84.3 %, and so on. Using
+            values other than 0.68, 0.9, 0.95, 0.99, 1, 2, 3, 4, 5 require the
+            scipy module.
         ncall : int or None, optional
             Limit the number of calls made by Minos. If None, an adaptive internal
             heuristic of the Minuit2 library is used (Default: None).