docs: 2.2 release annonuncement updated

docs/blog/posts/2.2.0-released.md

@@ -260,6 +260,16 @@ named with its corresponding unit and with the `si::zeroth_degree_Celsius`
 
 ## Changes to units definitions
 
+There were several known issues when units were deriving from each other
+(e.g., [#512](https://github.com/mpusz/mp-units/issues/512) and
+[#537](https://github.com/mpusz/mp-units/issues/537)). We could either highly complicate the
+framework to allow these which could result in much longer compilation times or disallow inheriting
+from units at all. We chose the second option.
+
+With this release all of of the units must be marked as `final`. To enforce this we have changed
+the definition of the `Unit<T>` concept, which now requires type `T` to be `final`
+(:boom: **breaking change** :boom:).
+
 [WG21 Study Group 16 (Unicode) raised concerns](https://github.com/sg16-unicode/sg16-meetings#january-24th-2024)
 about potential ABI issues when different translation units are compiled with different ordinary
 literal encodings. Those issues were resolved with a change to units definitions
@@ -272,7 +282,7 @@ is why it was renamed to `symbol_text` (:boom: **breaking change** :boom:).
 === "Now"
 
     ```cpp
-    inline constexpr struct ohm : named_unit<symbol_text{u8"Ω", "ohm"}, volt / ampere> {} ohm;
+    inline constexpr struct ohm final : named_unit<symbol_text{u8"Ω", "ohm"}, volt / ampere> {} ohm;
     ```
 
 === "Before"
@@ -286,7 +296,7 @@ is why it was renamed to `symbol_text` (:boom: **breaking change** :boom:).
     On C++20-compliant compilers it should be enough to type the following in the unit's definition:
 
     ```cpp
-    inline constexpr struct ohm : named_unit<{u8"Ω", "ohm"}, volt / ampere> {} ohm;
+    inline constexpr struct ohm final : named_unit<{u8"Ω", "ohm"}, volt / ampere> {} ohm;
     ```
 
 ## Improved text output
@@ -461,8 +471,8 @@ conversion factor. Here is a comparison of the code with previous and current de
 === "Now"
 
     ```cpp
-    inline constexpr struct yard : named_unit<"yd", mag_ratio<9'144, 10'000> * si::metre> {} yard;
-    inline constexpr struct foot : named_unit<"ft", mag_ratio<1, 3> * yard> {} foot;
+    inline constexpr struct yard final : named_unit<"yd", mag_ratio<9'144, 10'000> * si::metre> {} yard;
+    inline constexpr struct foot final : named_unit<"ft", mag_ratio<1, 3> * yard> {} foot;
     ```
 
 === "Before"