Documentation: increase example cache timeout to 1 hour

Previously, the example *decreased* the cache timeout compared to the
default, making it less user friendly.

Instead, nudge users to make cache more usable. Many users choose
store over cache.
https://lore.kernel.org/git/CAGJzqskRYN49SeS8kSEN5-vbB_Jt1QvAV9QhS6zNuKh0u8wxPQ@mail.gmail.com/

The default timeout remains 15 minutes. A stronger nudge would
be to increase that.

Signed-off-by: M Hickford <mirth.hickford@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

Documentation/git-credential-cache.txt

@@ -69,10 +69,10 @@ $ git push http://example.com/repo.git
 ------------------------------------
 
 You can provide options via the credential.helper configuration
-variable (this example drops the cache time to 5 minutes):
+variable (this example increases the cache time to 1 hour):
 
 -------------------------------------------------------
-$ git config credential.helper 'cache --timeout=300'
+$ git config credential.helper 'cache --timeout=3600'
 -------------------------------------------------------
 
 GIT