Fix: include custom dir so everybody has it.

.gitignore

@@ -1,7 +1,6 @@
 htdocs/conf/conf.php
 htdocs/conf/conf.php.old
 documents/
-custom/
 custom2/
 test/report/
 nbproject

htdocs/custom/README.md

@@ -0,0 +1,24 @@
+# DOLIBARR ERP & CRM custom directory for external modules.
+
+This directory is dedicated to store external modules.
+To use it, just copy here the directory of the module into this directory.
+
+Note: On linux or MAC systems, it is better to unzip/store the external module directory into 
+a different place than this directory and just adding a symbolic link here to the htdocs directory
+of the module.
+
+For example on Linux OS: Get the module from the command 
+mkdir ~/git; cd ~/git
+git clone https://git.doliforge.org/p/newmodule/newmodule.git
+Then create the symbolic link
+ln -fs ~/git/newmodule/htdocs /path_to_dolibarr/htdocs/custom/newmodule 
+
+WARNING !!!
+You must also enable the custom directory into dolibarr conf/conf.php file by adding the following 
+two lines, so dolibarr will also scan this directories to find external external modules:
+
+$dolibarr_main_url_root_alt='/custom';
+$dolibarr_main_document_root_alt='/path_to_dolibarr/htdocs/custom/';
+
+(This is not enabled by default because enabling external module may slow down application)
+