runtime(doc): Recover some missed commas and periods in starting.txt

runtime(doc): Recover some missed commas and periods in starting.txt

Also:

- Insert some missing words;
- Strive for consistency with capitalisation of words;
- Improve shell alias examples.

The gvim words were left alone for now, but they deserve to
be treated like proper names, GVim or GUI Vim, unless these
refer to executable filenames (on *nix systems).

closes: #14194

Signed-off-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>