Add introductory paragraphs for maintainers and ESC

Add an introductory paragraph, taken from the project governance
documentation in the core Gerrit project, and add links to the
full documentation that is hosted on gerrit-review.

In later changes we may consider moving the entire governance
documentation from core Gerrit to the homepage, but this is beyond
the scope of the current change.

Change-Id: I9617f4622066abc3661d0d8a20cf8ceff108ed6c
diff --git a/pages/site/members.md b/pages/site/members.md
index ee93a2d..a11d63f 100644
--- a/pages/site/members.md
+++ b/pages/site/members.md
@@ -8,7 +8,11 @@
 
 ## Engineering Steering Committee
 
-Members of the Engineering Steering Committee (ESC) for the 2019 term are:
+The Gerrit project has an Engineering Steering Committee (ESC) that
+governs the project. For details about the role of the ESC, refer to the
+[description here](https://gerrit-review.googlesource.com/Documentation/dev-processes.html#steering-committee).
+
+Members of the ESC for the 2019 term are:
 
 | Name                  | Affiliation            |
 |-----------------------|------------------------|
@@ -20,6 +24,11 @@
 
 ## Maintainers
 
+Maintainers are the gatekeepers of the project and are in charge of approving
+and submitting changes. For more details about the role of maintainers, refer
+to the
+[description here](https://gerrit-review.googlesource.com/Documentation/dev-roles.html#maintainer).
+
 Current maintainers are:
 
 | Name                  |