Updates README and documentation

Author: steve-perkins

README.md

@@ -134,7 +134,8 @@ Note that changes to the major version (i.e. the first number) represent possibl
 may require modifications in your code to migrate.  Changes to the minor version (i.e. the second number)
 should represent non-breaking changes.  The third number represents any very minor bugfix patches.
 
-* **2.0.0 (in progress)**: Adds support for authentication via the AppRole auth backend.
+* **2.0.0 (in progress)**: Adds support for authentication via the AppRole auth backend.  Adds support for 
+                             renewing secret leases.
 * **1.2.0**: This is a substantial release, with numerous additions.  It's a minor version number only because there 
              should be no breaking changes.  The changes include the following:
   * Switches from Vault 0.5.x to 0.6.x for automated tests.  

src/main/java/com/bettercloud/vault/api/Leases.java

@@ -202,6 +202,14 @@ public VaultResponse revokeForce(final String prefix) throws VaultException {
      * @throws VaultException The response information returned from Vault
      */
     public VaultResponse renew(final String leaseId, final long increment) throws VaultException {
+
+        // TODO:  Unfortunately, there is not currently a way to cover this in the integration test suite.
+        //        The "generic" backend does not support support lease renewal.  The only other backend
+        //        currently available to the integration test suite is the "pki" backend, which does
+        //        support renewal of credentials, etc.  But lease renewal in this context is talking about
+        //        secrets.  Perhaps revisit this at some point in the future if other backends are available
+        //        to the integration test suite (e.g. if we eventually start using Docker).
+
         int retryCount = 0;
         while (true) {
             try {