DOC: Add signature file build information

Author: HaoZeke

doc/source/f2py/buildtools/cmake.rst

@@ -18,8 +18,8 @@ but the `official CMake Tutorials`_ are a fantastic resource.
    ``f2py`` is not particularly native or pleasant; and a more natural approach
    is to consider :ref:`f2py-skbuild`
 
-Fibonacci Walkthrough
-=======================
+Fibonacci Walkthrough (F77)
+===========================
 
 Returning to the ``fib``  example from :ref:`f2py-getting-started` section.
 

doc/source/f2py/buildtools/index.rst

@@ -37,7 +37,7 @@ Building an extension module which includes Python and Fortran consists of:
 
 - Python libraries and development headers
 
-Broadly speaking there are two cases which arise when considering the outputs of ``f2py``:
+Broadly speaking there are three cases which arise when considering the outputs of ``f2py``:
 
 Fortran 77 programs
    - Input file ``blah.f``
@@ -48,15 +48,30 @@ Fortran 77 programs
 Fortran 90 programs
    - Input file ``blah.f``
    - Generates:
+
      + ``blahmodule.c``
      + ``blah-f2pywrappers2.f90``
 
    The secondary wrapper is used to handle code which is subdivided into modules.
 
+Signature files
+   - Input file ``blah.pyf``
+   - Generates:
+
+     + ``blahmodule.c``
+     + ``blah-f2pywrappers2.f90`` (occasionally)
+
+   Signature files ``.pyf`` do not signal their language standard via the file extension, they may generate the module wrapper depending on their contents; which shifts the burden of checking for generated files onto the build system.
+
+
 In theory keeping the above requirements in hand, any build system can be
 adapted to generate ``f2py`` extension modules. Here we will cover a subset of
 the more popular systems.
 
+.. note::
+   ``make`` has no place in a modern multi-language setup, and so is not
+   discussed further.
+
 Build Systems
 ==============
 
@@ -67,7 +82,3 @@ Build Systems
    meson
    cmake
    skbuild
-
-.. note::
-   ``make`` has no place in a modern multi-language setup, and so is not
-   discussed further.

doc/source/f2py/buildtools/meson.rst

@@ -14,8 +14,8 @@ comfortable and amenable to extension for ``python`` users.
     Meson needs to be at-least ``0.46.0`` in order to resolve the ``python`` include directories.
 
 
-Fibonacci Walkthrough
-=======================
+Fibonacci Walkthrough (F77)
+===========================
 
 
 We will need the generated ``C`` wrapper before we can use a general purpose

doc/source/f2py/buildtools/skbuild.rst

@@ -19,8 +19,8 @@ For situations where no ``setuptools`` replacements are required or wanted (i.e.
 if ``wheels`` are not needed), it is recommended to instead use the vanilla
 ``cmake`` setup described in :ref:`f2py-cmake`.
 
-Fibonacci Walkthrough
-=======================
+Fibonacci Walkthrough (F77)
+===========================
 
 We will consider the ``fib``  example from :ref:`f2py-getting-started` section.