There is not a dedicated pull hook, but every pull (that has content to pull in) performs a merge. There is a post-merge hook. Since you only need to warn to check external components when the code base has been updated therfore this is correct for the situation.
Hooks are just specially named executable scripts inside your .git/hooks
folder
touch .git/hooks/post-merge
chmod u+x .git/hooks/post-merge
vim .git/hooks/post-merge
#!/bin/sh
echo "Hey, you should run `bower install` after this pull"
Hooks are not part of the repository though and therefore not distributed. One method of dealing with this is to create a controlled hooks folder and a script which symlinks them.
bin/create-hook-symlinks
hooks/post-merge
Where post-merge is the file you have already created, the linking script would be:
touch bin/create-hook-symlinks
chmod u+x bin/create-hook-symlinks
vim bin/create-hook-symlinks
#!/bin/sh
ln hooks/post-merge .git/hooks/post-merge
On OS X I could not get the soft-link to execute, updated to hardlink.
Linked Question Is there any git hook for pull?
More info Git hook Docs & Hook tutorial.