document the "include" mechanism

conf/example.conf

@@ -246,3 +246,16 @@ repo gitolite
 # This does either a plain "git config section.key value" (for the first 3
 # examples above) or "git config --unset-all section.key" (for the last
 # example).  Other forms (--add, the value_regex, etc) are not supported.
+
+# INCLUDE SOME OTHER FILE
+# -----------------------
+
+    include     "foo.conf"
+
+# this includes the contents of $GL_ADMINDIR/conf/foo.conf here
+
+# Notes:
+# - the include statement is not allowed inside delegated fragments for
+#   security reasons.
+# - you can also use an absolute path if you like, although in the interests
+#   of cloning the admin-repo sanely you should avoid doing this!

doc/3-faq-tips-etc.mkd

@@ -15,6 +15,7 @@ In this document:
       * two levels of access rights checking
       * file/dir NAME based restrictions
       * error checking the config file
+      * including config lines from other files
       * delegating parts of the config file
       * easier to specify gitweb "description" and gitweb/daemon access
       * easier to link gitweb authorisation with gitolite
@@ -254,6 +255,10 @@ was denied.
 Gitolite "compiles" the config file first and keyword typos *are* caught so
 you know right away.
 
+#### including config lines from other files
+
+See the entry under "INCLUDE SOME OTHER FILE" in `conf/example.conf`.
+
 #### delegating parts of the config file
 
 You can now split up the config file and delegate the authority to specify