[doc] Add README and package-info to the SSH bundles

Explain in the JSch bundle that it is essentially unmaintained. Add
descriptions in both bundles explaining how to use it, or how to use
an alternate implementation.

Change-Id: Idaf46c33b14543279f78a55cb7c6bd42b06ee6b8
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

2 files changed, 73 insertions, 0 deletions

diff --git a/org.eclipse.jgit.ssh.jsch/README.md b/org.eclipse.jgit.ssh.jsch/README.md
new file mode 100644
index 0000000000..48f43f0f87
--- /dev/null
+++ b/org.eclipse.jgit.ssh.jsch/README.md
@@ -0,0 +1,59 @@
+# JGit SSH support via JSch
+
+This bundle provides an implementation of git transport over SSH implemented via JSch.
+
+**This bundle should be considered deprecated**. It is essentially unmaintained, and
+the JGit project may decide anytime to remove it completely without further ado.
+
+The officially supported SSH transport is in bundle `org.eclipse.jgit.ssh.apache` and is
+built upon [Apache MINA sshd](https://mina.apache.org/sshd-project/).
+
+## Service registration
+
+This bundle declares a service for the `java.util.ServiceLoader` for interface
+`org.eclipse.jgit.transport.ssh.SshSessionFactory`. The core JGit bundle uses the service
+loader to pick up an implementation of that interface. The bundle in an OSGi fragment
+to ensure that the service loader works in an OSGi environment without the need to
+install a service loader bridge.
+
+Note that JGit simply uses the first `SshSessionFactory` provided by the `ServiceLoader`.
+
+## Using a different SSH implementation
+
+To use a different SSH implementation:
+
+* Do not include this bundle in your product.
+* Include the bundle of the alternate implementation.
+    * If the service loader finds the alternate implementation, nothing more is needed.
+    * Otherwise ensure the service declaration from the other bundle is on the Classpath of bundle `org.eclipse.jgit`,
+    * or set the `SshSessionFactory` for JGit explicitly (see below).
+
+## Configuring an SSH implementation for JGit
+
+The simplest way to set an SSH implementation for JGit is to install it globally via
+`SshSessionFactory.setInstance()`. This instance will be used by JGit for all SSH
+connections by default.
+
+It is also possible to set the SSH implementation individually for any git command
+that needs a transport (`TransportCommand`) via a `org.eclipse.jgit.api.TransportConfigCallback`.
+
+To do so, set the wanted `SshSessionFactory` on the SSH transport, like:
+
+```java
+SshSessionFactory customFactory = ...; // Get it from wherever
+FetchCommand fetch = git.fetch()
+  .setTransportConfigCallback(transport -> {
+    if (transport instanceof SshTransport) {
+      ((SshTransport) transport).setSshSessionFactory(customFactory);
+    }
+  })
+  ...
+  .call();
+```
+
+## Using an external SSH executable
+
+JGit has built-in support for not using any Java SSH implementation but an external SSH
+executable. To use an external SSH executable, set environment variable **GIT_SSH** to
+the path of the executable. JGit will create a sub-process to run the executable and
+communicate with this sup-process to perform the git operation.
diff --git a/org.eclipse.jgit.ssh.jsch/src/org/eclipse/jgit/transport/ssh/jsch/package-info.java b/org.eclipse.jgit.ssh.jsch/src/org/eclipse/jgit/transport/ssh/jsch/package-info.java
new file mode 100644
index 0000000000..dc2915a09f
--- /dev/null
+++ b/org.eclipse.jgit.ssh.jsch/src/org/eclipse/jgit/transport/ssh/jsch/package-info.java
@@ -0,0 +1,14 @@
+/**
+ * Provides a JGit {@link org.eclipse.jgit.transport.SshSessionFactory}
+ * implemented via JSch.
+ * <p>
+ * This package should be considered <b>deprecated</b>. It is essentially
+ * unmaintained and the JGit project may decide to remove it completely without
+ * further ado at any time.
+ * </p>
+ * <p>
+ * The officially supported Java SSH implementation for JGit is in bundle
+ * {@code org.eclipse.jgit.ssh.apache} and is built upon
+ * <a href="https://mina.apache.org/sshd-project/">Apache MINA sshd</a>.
+ */
+package org.eclipse.jgit.transport.ssh.jsch;