Documentation/remote-helpers: Add invocation section

index 15214ae..25a0a16 100644
@@ -7,7 +7,7 @@ git-remote-helpers - Helper programs to interact with remote repositories
 
 SYNOPSIS
 --------
-'git remote-<transport>' <remote>
+'git remote-<transport>' <repository> [<URL>]
 
 DESCRIPTION
 -----------

@@ -38,6 +38,35 @@ transport protocols, such as 'git-remote-http', 'git-remote-https',
 'git-remote-ftp' and 'git-remote-ftps'. They implement the capabilities
 'fetch', 'option', and 'push'.
 
+INVOCATION
+----------
+
+Remote helper programs are invoked with one or (optionally) two
+arguments. The first argument specifies a remote repository as in git;
+it is either the name of a configured remote or a URL. The second
+argument specifies a URL of the form '<transport>://<address>' or
+'<transport>::<address>', where '<address>' may be an arbitrary
+string.
+
+When git encounters a URL of the form '<transport>://<address>', where
+'<transport>' is a protocol that it cannot handle natively, it
+automatically invokes 'git remote-<transport>' with the full URL as
+the second argument. If such a URL is encountered directly on the
+command line, the first argument is the same as the second, and if it
+is encountered in a configured remote, the first argument is the name
+of that remote.
+
+A URL of the form '<transport>::<address>' explicitly instructs git to
+invoke 'git remote-<transport>' with '<address>' as the second
+argument. If such a URL is encountered directly on the command line,
+the first argument is '<address>', and if it is encountered in a
+configured remote, the first argument is the name of that remote.
+
+Additionally, when a configured remote has 'remote.<name>.vcs' set to
+'<transport>', git explicitly invokes 'git remote-<transport>' with
+'<name>' as the first argument. If set, the second argument is
+'remote.<name>.url'; otherwise, the second argument is omitted.
+
 COMMANDS
 --------
 

@@ -211,6 +240,10 @@ OPTIONS
 	helper MUST NOT rely on this option being set before
 	connect request occurs.
 
+SEE ALSO
+--------
+linkgit:git-remote[1]
+
 Documentation
 -------------
 Documentation by Daniel Barkalow and Ilari Liusvaara