Install it in one of the directories pointed to by
bash-completion's pkgconfig file variables.  There are two
alternatives: the recommended one is 'completionsdir' (get it with
"pkg-config --variable=completionsdir bash-completion") from which
completions are loaded on demand based on invoked commands' names,
so be sure to name your completion file accordingly, and to include
for example symbolic links in case the file provides completions
for more than one command.  The other one which is present for
backwards compatibility reasons is 'compatdir' (get it with
"pkg-config --variable=compatdir bash-completion") from which files
are loaded when bash_completion is loaded.

For packages using GNU autotools the installation can be handled
for example like this in configure.ac:

 PKG_CHECK_VAR(bashcompdir, [bash-completion], [completionsdir], ,
   bashcompdir="${sysconfdir}/bash_completion.d")
 AC_SUBST(bashcompdir)

...accompanied by this in Makefile.am:

 bashcompdir = @bashcompdir@
 dist_bashcomp_DATA = # completion files go here

For cmake we ship the bash-completion-config.cmake and
bash-completion-config-version.cmake files. Example usage:

 find_package(bash-completion)
 if(BASH_COMPLETION_FOUND)
   message(STATUS
     "Using bash completion dir ${BASH_COMPLETION_COMPLETIONSDIR}")
 else()
   set (BASH_COMPLETION_COMPLETIONSDIR "/etc/bash_completion.d")
   message (STATUS
     "Using fallback bash completion dir ${BASH_COMPLETION_COMPLETIONSDIR}")
 endif()

 install(FILES your-completion-file DESTINATION
   ${BASH_COMPLETION_COMPLETIONSDIR})

 set show-all-if-ambiguous on

 set page-completions off