docs: import std; row added to the "C++ compiler support" table

docs/getting_started/cpp_compiler_support.md

@@ -18,6 +18,7 @@ C++ feature:
 | **Minimum support**                                       |     20      |  12  |  16   |     15      | None |
 | **`std::format`**                                         |     20      |  13  |  17   |    None     | None |
 | **C++ modules**                                           |     20      | None |  17   |    None     | None |
+| **`import std;`**                                         |     23      | None |  18   |    None     | None |
 | **Static `constexpr` variables in `constexpr` functions** |     23      |  13  |  17   |    None     | None |
 | **Explicit `this` parameter**                             |     23      |  14  |  18   |    None     | None |
 
@@ -62,6 +63,15 @@ C++ feature:
     [CMake's documentation](https://cmake.org/cmake/help/latest/manual/cmake-cxxmodules.7.html).
 
 
+## `import std;`
+
+- If enabled, the library will obtain all the definitions from the `std` namespace via
+  `import std;` instead of the "old-style" header includes.
+- Related build options:
+    - Conan: [import_std](installation_and_usage.md#import_std)
+    - CMake: [MP_UNITS_BUILD_IMPORT_STD](installation_and_usage.md#MP_UNITS_BUILD_IMPORT_STD)
+
+
 ## Static `constexpr` variables in `constexpr` functions
 
 - Allows returning `std::string_view` from the