précision pour éviter les erreurs mémoires pour composer

docs/installation.md

@@ -114,4 +114,9 @@ If you creating an element you ahev the issue "cannot load method bcmod from nam
 You need to install the bc-math module
 ```
 sudo apt install php7.0-bcmath
+```
+
+If memory limits while using composer
+```
+COMPOSER_MEMORY_LIMIT=-1 composer ...
 ```
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