DOC: timeout client: pointers to timeout http-request

It worth mentionning "timeout http-request" in the "timeout client"
documentation paragraph, to ensure nobody misses this important setting.

backport: 1.5 and above
(cherry picked from commit 2e1941ec6e0a88a7681883b409b538fbd3dcbba5)
(cherry picked from commit d4a0c4140e81dd21c0c73fcb159be1f2797eb534)
1 file changed