Add convenience method to authenticate with app installation tokens;

Convert existing markdown doc to APT due to formatting features;
Replace occurrences of kohsuke user to github-api org where applicable;
Fix repositoryIds method on GHAppCreateTokenBuilder;

Signed-off-by: PauloMigAlmeida <paulo.miguel.almeida.rodenas@gmail.com>

src/test/java/org/kohsuke/github/GitHubConnectionTest.java

@@ -46,7 +46,6 @@ public class GitHubConnectionTest extends AbstractGitHubWireMockTest {
         GitHub hub = GitHub.connectUsingPassword("kohsuke", "bogus");
         assertEquals("https://api.github.com/test", hub.getApiURL("/test").toString());
     }
-
     @Test
     public void testGitHubBuilderFromEnvironment() throws IOException {
 
@@ -86,6 +85,17 @@ public class GitHubConnectionTest extends AbstractGitHubWireMockTest {
         assertEquals("bogusPassword", builder.password);
         assertEquals("bogusEndpoint", builder.endpoint);
     }
+    @Test
+    public void testGithubBuilderWithAppInstallationToken() throws Exception{
+        GitHubBuilder builder = new GitHubBuilder().withAppInstallationToken("bogus");
+        assertEquals("bogus", builder.oauthToken);
+        assertEquals("", builder.user);
+
+        // test authorization header is set as in the RFC6749
+        GitHub github = builder.build();
+        assertEquals("token bogus",github.encodedAuthorization);
+        assertEquals("",github.login);
+    }
 
     @Test
     public void testGitHubRateLimit() throws Exception {