Documentation: clarify multiple pushurls vs urls

In a remote with multiple configured URLs, `git remote -v` shows the
correct url that fetch uses. However, `git config remote.<remote>.url`
returns the last defined url instead. This discrepancy can cause
confusion for users with a remote defined as such, since any url
defined after the first essentially acts as a pushurl.

Add documentation to clarify how fetch interacts with multiple urls
and how push interacts with multiple pushurls and urls.

Add test affirming interaction between fetch and multiple urls.

Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/urls-remotes.txt

@@ -33,7 +33,9 @@ config file would appear like this:
 ------------
 
 The `<pushurl>` is used for pushes only. It is optional and defaults
-to `<URL>`.
+to `<URL>`. Pushing to a remote affects all defined pushurls or to all
+defined urls if no pushurls are defined. Fetch, however, will only
+fetch from the first defined url if muliple urls are defined.
 
 Named file in `$GIT_DIR/remotes`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

t/t5510-fetch.sh

@@ -806,6 +806,14 @@ test_expect_success 'fetch.writeCommitGraph with submodules' '
 	)
 '
 
+# fetches from first configured url
+test_expect_success 'fetch from multiple configured URLs in single remote' '
+	git init url1 &&
+	git remote add multipleurls url1 &&
+	git remote set-url --add multipleurls url2 &&
+	git fetch multipleurls
+'
+
 # configured prune tests
 
 set_config_tristate () {