[Rd] Demo folder and 00Index file format

[Gorjanc Gregor]

Hi!

Columns in demo/00Index must be separated with at least 3 spaces otherwise
the following WARNING is issued during R CMD check

...
* checking index information ... WARNING
Demos with missing or empty index information:
[1] "foo"
...

After a search I found out that this is noted in file

src/library/tools/R/read.00Index.R

I suggest to update the manual in the following way.

Regards, Gregor

Index: doc/manual/R-exts.texi
===================================================================
--- doc/manual/R-exts.texi      (revision 42745)
+++ doc/manual/R-exts.texi      (working copy)
@@ -560,8 +560,8 @@
 of the extensions @file{.R} or @file{.r}.  If present, the @file{demo}
 subdirectory should also have a @file{00Index} file with one line for
 each demo, giving its name and a description separated by white
-space. (Note that it is not possible to generate this index file
-automatically.)
+space - at least 3 spaces or 1 tab. (Note that it is not possible to
+generate this index file automatically.)