[gtkmm] Convert README to README.md

[Kjell Ahlstedt <kjellahl src gnome org>]

commit cc2ff7ce952f711847eb0e42785991e7f4a5a385
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Tue Sep 13 09:54:57 2022 +0200

    Convert README to README.md

 README => README.md | 42 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 6 deletions(-)
---
diff --git a/README b/README.md
similarity index 90%
rename from README
rename to README.md
index b687ba0b..aa374a8f 100644
--- a/README
+++ b/README.md
@@ -1,3 +1,4 @@
+# gtkmm
 This is gtkmm, the C++ API for GTK. 
 See http://www.gtkmm.org/
 
@@ -13,9 +14,10 @@ See README.win32
 ## Building from a release tarball
 
 Extract the tarball and go to the extracted directory:
+```
   $ tar xf gtkmm-@GTKMM_VERSION  tar xz
   $ cd gtkmm-@GTKMM_VERSION@
-
+```
 It's easiest to build with Meson, if the tarball was made with Meson,
 and to build with Autotools, if the tarball was made with Autotools.
 Then you don't have to use maintainer-mode.
@@ -28,31 +30,46 @@ other subdirectories of untracked/.
 
 Don't call the builddir 'build'. There is a directory called 'build' with
 files used by Autotools.
-
+```
   $ meson --prefix /some_directory --libdir lib your_builddir .
   $ cd your_builddir
+```
 
 If the tarball was made with Autotools, you must enable maintainer-mode:
+```
   $ meson configure -Dmaintainer-mode=true
+```
 
 Then, regardless of how the tarball was made:
+```
   $ ninja
   $ ninja install
+```
 You can run the tests like so:
+```
   $ ninja test
+```
 
 ### Building from a tarball with Autotools
 
 If the tarball was made with Autotools:
+```
   $ ./configure --prefix=/some_directory
+```
 If the tarball was made with Meson, you must enable maintainer-mode:
+```
   $ ./autogen.sh --prefix=/some_directory
+```
 
 Then, regardless of how the tarball was made:
+```
   $ make
   $ make install
+```
 You can build the examples and tests, and run some of the tests, like so:
+```
   $ make check
+```
 
 ## Building from git
 
@@ -60,8 +77,9 @@ Building from git can be difficult so you should prefer building from
 a release tarball unless you need to work on the gtkmm code itself.
 
 jhbuild can be a good help
-  https://gitlab.gnome.org/GNOME/jhbuild
-  https://wiki.gnome.org/Projects/Jhbuild
+- https://gitlab.gnome.org/GNOME/jhbuild
+- https://wiki.gnome.org/Projects/Jhbuild
+- https://gnome.pages.gitlab.gnome.org/jhbuild
 
 ### Building from git with Meson
 
@@ -69,24 +87,36 @@ Maintainer-mode is enabled by default when you build from a git clone.
 
 Don't call the builddir 'build'. There is a directory called 'build' with
 files used by Autotools.
-
+```
   $ meson --prefix /some_directory --libdir lib your_builddir .
   $ cd your_builddir
   $ ninja
   $ ninja install
+```
 You can run the tests like so:
+```
   $ ninja test
+```
 You can create a tarball like so:
+```
   $ ninja dist
+```
 
 ### Building from git with Autotools
-
+```
   $ ./autogen.sh --prefix=/some_directory
   $ make
   $ make install
+```
 You can build the examples and tests, and run some of the tests, like so:
+```
   $ make check
+```
 You can create a tarball like so:
+```
   $ make distcheck
+```
 or
+```
   $ make dist
+```