Fix lost files in custom

htdocs/custom/.gitignore

@@ -0,0 +1,4 @@
+/*
+!.gitignore
+!README.md
+!index.html

htdocs/custom/README.md

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+# 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.framasoft.org/p/newmodule/newmodule.git`
+
+Then create the symbolic link
+
+`ln -fs ~/git/newmodule/htdocs /path_to_dolibarr/htdocs/custom/newmodule`
+
+WARNING !!!
+Check also that the /custom directory is active by adding into dolibarr `conf/conf.php` file the following
+two lines, so dolibarr will also scan /custom directory to find external external modules:
+
+```php
+$dolibarr_main_url_root_alt='/custom';
+$dolibarr_main_document_root_alt='/path_to_dolibarr/htdocs/custom/';
+```