Update documentation with FreeBSD build instructions

docs/reference/glib/building.xml

@@ -26,6 +26,12 @@
         <userinput>ninja -C _build</userinput>
         <userinput>ninja -C _build install</userinput>
       </literallayout>
+
+      On FreeBSD:
+      <literallayout>
+        <userinput>env CPPFLAGS="-I/usr/local/include" LDFLAGS="-L/usr/local/lib -Wl,--disable-new-dtags" meson -Dxattr=false -Dinstalled_tests=true -Diconv=external -Db_lundef=false _build</userinput>
+        <userinput>ninja -C _build</userinput>
+      </literallayout>
     </para>
 
     <para>
@@ -119,6 +125,16 @@
           operating systems as well.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          Python 3.5 or newer is required. Your system Python must
+          conform to <ulink
+          url="https://www.python.org/dev/peps/pep-0394/">PEP 394
+          </ulink>
+          For FreeBSD, this means that the
+          <literal>lang/python3</literal> port must be installed.
+        </para>
+      </listitem>
       <listitem>
         <para>
           The libintl library from the <ulink