Update documentation to add --exclude option to eclipse script

Generating the eclipse project puts both servlet-api_2_5 and
servlet-api_3_0 in the classpath. We only need the latter in order
to run gitiles from eclipse. Having servlet-api_2_5 in the classpath
(in front of the servlet-api_3_0) produces errors and doesn't find
css styles.

The servlet-api_2_5 can be excluded by the --exclude option on the
eclipse script. Update the documentation to mention this.

Change-Id: I2174e46775519d7dc72422d69ebda9f0d8c1f1c3

Documentation/developer-guide.md

diff --git a/Documentation/developer-guide.md b/Documentation/developer-guide.md
index 2d4af0f..59a36f9 100644
--- a/Documentation/developer-guide.md
+++ b/Documentation/developer-guide.md
@@ -39,7 +39,7 @@
 If you'd like to use Eclipse to edit Gitiles, first generate a project file:
 
 ```
-./bucklets/tools/eclipse.py --src
+./bucklets/tools/eclipse.py --src --exclude=servlet-api_2_5
 ```
 
 Import the project in Eclipse: