bug#7515: [wishlist] Info Elisp::call-process -- Add process run directory information

[Glenn Morris]

> Please add documentation to info page Elisp::call-process
>
>     37.3 Creating a Synchronous Process
>
> What variable affects the location where process is being run:

37.1 Functions that Create Subprocesses

  Synchronous and asynchronous processes are explained in the
following sections. Since the three functions are all called in a
similar fashion, their common arguments are described here.

[...]

   The subprocess gets its current directory from the value of
`default-directory' (*note File Name Expansion::).