nls: Add Slovak translation.

* po/packages/sk.po: New file.
* po/packages/LINGUAS: Add 'sk'.
* po/doc/guix-manual.sk.po: New file.
* doc/local.mk (info_TEXINFOS): Add it.
* po/doc/local.mk (DOC_PO_FILES): Add it.

doc/local.mk

@@ -27,6 +27,7 @@ info_TEXINFOS = %D%/guix.texi			\
   %D%/guix.fr.texi				\
   %D%/guix.pt_BR.texi				\
   %D%/guix.ru.texi				\
+  %D%/guix.sk.texi				\
   %D%/guix.zh_CN.texi				\
   %D%/guix-cookbook.texi			\
   %D%/guix-cookbook.de.texi			\

po/doc/local.mk

@@ -22,6 +22,7 @@ DOC_PO_FILES=					\
   %D%/guix-manual.fr.po				\
   %D%/guix-manual.pt_BR.po			\
   %D%/guix-manual.ru.po				\
+  %D%/guix-manual.sk.po				\
   %D%/guix-manual.zh_CN.po
 
 DOC_COOKBOOK_PO_FILES=					\

po/packages/LINGUAS

@@ -10,6 +10,7 @@ fr
 hu
 pl
 pt_BR
+sk
 sr
 vi
 zh_CN