Add draft cohorts page and update xrefs

Author: mborland

doc/modules/ROOT/nav.adoc

@@ -27,6 +27,7 @@
 ** xref:decimal_fast32_t.adoc[]
 ** xref:decimal_fast64_t.adoc[]
 ** xref:decimal_fast128_t.adoc[]
+* xref:cohorts.adoc[]
 * xref:conversions.adoc[]
 * xref:literals.adoc[]
 * xref:numbers.adoc[]

doc/modules/ROOT/pages/cmath.adoc

@@ -679,7 +679,7 @@ constexpr Decimal normalize(Decimal val) noexcept;
 ----
 
 Similar to the `frexp10` function above, but rather than returning the normalized significand, and exponent of the Decimal number, it returns a normalized number.
-This removes the effects of xref:basics.adoc[cohorts] on the IEEE 754 compliant types.
+This removes the effects of xref:cohorts.adoc[cohorts] on the IEEE 754 compliant types which for the example of `decimal32_t` means the significand will be in the range [1'000'000, 9'999'999].
 This function has *NO* effect on fast types since they are always normalized internally.
 
 === `rescale`

doc/modules/ROOT/pages/cohorts.adoc

@@ -0,0 +1,9 @@
+////
+Copyright 2025 Matt Borland
+Distributed under the Boost Software License, Version 1.0.
+https://www.boost.org/LICENSE_1_0.txt
+////
+
+[#cohorts]
+= Cohorts
+:idprefix: cohorts_