Fix PROJ_DOWNLOAD_DIR-setting code examples
Fix PROJ_DOWNLOAD_DIR-setting code examples

The examples which set the `PROJ_DOWNLOAD_DIR` environment variable were
syntactically incorrect because there was no closing double quotes
accompanying the `python -c` command and the closing parens of the
command substitution was missing.  Now these commands work as expected
when copy-pasting them into the terminal.

ocefpaf/pyproj,ocefpaf/pyproj,pyproj4/pyproj,pyproj4/pyproj