vim_getenv: $VIMRUNTIME fallback: ../share/nvim/runtime (#6223)

Do this on all systems, so that portable builds work everywhere. This
allows us to ship archives with this folder structure:

    bin/nvim
    share/nvim/runtime

then ./bin/nvim works without the user needing to explicitly set VIMRUNTIME.

1 files changed, 2 insertions, 7 deletions

diff --git a/runtime/doc/starting.txt b/runtime/doc/starting.txt
index 9284aaea58..2c024d3c75 100644
--- a/runtime/doc/starting.txt
+++ b/runtime/doc/starting.txt
@@ -657,15 +657,10 @@ is the order used to find the value of $VIMRUNTIME:
 3. If "$VIM/runtime" exists, it is used.
 4. The value of $VIM is used.  This is for backwards compatibility with older
    versions.
-5. When the 'helpfile' option is set and doesn't contain a '$', its value is
+5. If "../share/nvim/runtime" exists relative to |v:progpath|, it is used.
+6. When the 'helpfile' option is set and doesn't contain a '$', its value is
    used, with "doc/help.txt" removed from the end.
 
-For Unix, when there is a compiled-in default for $VIMRUNTIME (check the
-output of ":version"), steps 2, 3 and 4 are skipped, and the compiled-in
-default is used after step 5.  This means that the compiled-in default
-overrules the value of $VIM.  This is useful if $VIM is "/etc" and the runtime
-files are in "/usr/share/vim/vim54".
-
 Once Vim has done this once, it will set the $VIMRUNTIME environment variable.
 To change it later, use a ":let" command like this: >
 	:let $VIMRUNTIME = "/home/piet/vim/vim54"