[COMMITTED] fix 'make distcheck'

[Bruno Haible]

Hi,

The CI failed in "make distcheck":

Making all in doc
make[2]: Entering directory 
'/builds/gnu-poke/ci-distcheck/poke/poke-0.1-20200330-beta/_build/sub/doc'
make[2]: *** No rule to make target '../../../doc/gen-pvm-insns.sh', needed by 
'pvm-insns.texi'.  Stop.

It is caused by
https://git.savannah.gnu.org/gitweb/?p=poke.git;a=commitdiff;h=043b9b98c816697a1c4a9e14ed533961f05bff20

For this, the fix is easy, in doc/Makefile.am.

2020-04-04  Bruno Haible  <address@hidden>

        Fix 'make distcheck'.
        * doc/Makefile.am (EXTRA_DIST): New variable.

diff --git a/doc/Makefile.am b/doc/Makefile.am
index b55038e..4c075ae 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -16,6 +16,8 @@
 info_TEXINFOS = poke.texi
 poke_TEXINFOS = fdl.texi pvm-insns.texi
 
+EXTRA_DIST = gen-pvm-insns.sh
+
 # The description of PVM instructions is generated from the
 # src/pvm.jitter file.