documentation: Use git config --file path

This is supported by much older versions of git, as well as the
bleeding edge development version.  Users are more likely to be
able to follow the instructions now, with any version of git.

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/Documentation/config-contact.txt b/Documentation/config-contact.txt
index bcad001..43a891b 100644
--- a/Documentation/config-contact.txt
+++ b/Documentation/config-contact.txt
@@ -80,8 +80,8 @@
 `contactstore.appsec`):
 
 ====
-  git config --file=$site_path/gerrit.config appsec.url https://...
-  git config --file=$site_path/gerrit.config appsec.appsec sekret
+  git config --file $site_path/gerrit.config appsec.url https://...
+  git config --file $site_path/gerrit.config appsec.appsec sekret
 ====
 
 
diff --git a/Documentation/config-gitweb.txt b/Documentation/config-gitweb.txt
index 416c34c..72cad7c 100644
--- a/Documentation/config-gitweb.txt
+++ b/Documentation/config-gitweb.txt
@@ -13,7 +13,7 @@
 namespace is available.
 
 ====
-  git config --file=$site_path/gerrit.config gitweb.url http://example.com/gitweb.cgi
+  git config --file $site_path/gerrit.config gitweb.url http://example.com/gitweb.cgi
 ====
 
 After updating `'$site_path'/gerrit.config`, the Gerrit server must
diff --git a/Documentation/config-sso.txt b/Documentation/config-sso.txt
index d2204ea..5b7b1ca 100644
--- a/Documentation/config-sso.txt
+++ b/Documentation/config-sso.txt
@@ -13,7 +13,7 @@
 setting should be `OpenID`:
 
 ====
-  git config --file=$site_path/gerrit.config auth.type OpenID
+  git config --file $site_path/gerrit.config auth.type OpenID
 ====
 
 As this is the default setting there is nothing required from the
@@ -85,9 +85,9 @@
 To enable this form of authentication:
 
 ====
-  git config --file=$site_path/gerrit.config auth.type HTTP
-  git config --file=$site_path/gerrit.config --unset auth.httpHeader
-  git config --file=$site_path/gerrit.config auth.emailFormat '{0}@example.com'
+  git config --file $site_path/gerrit.config auth.type HTTP
+  git config --file $site_path/gerrit.config --unset auth.httpHeader
+  git config --file $site_path/gerrit.config auth.emailFormat '{0}@example.com'
 ====
 
 The auth.type must always be HTTP, indicating the user identity
@@ -160,9 +160,9 @@
 To enable this form of authentication:
 
 ====
-  git config --file=$site_path/gerrit.config auth.type HTTP
-  git config --file=$site_path/gerrit.config auth.httpHeader SM_USER
-  git config --file=$site_path/gerrit.config auth.emailFormat '{0}@example.com'
+  git config --file $site_path/gerrit.config auth.type HTTP
+  git config --file $site_path/gerrit.config auth.httpHeader SM_USER
+  git config --file $site_path/gerrit.config auth.emailFormat '{0}@example.com'
 ====
 
 The auth.type must always be HTTP, indicating the user identity