Add required php extensions for psalm

Signed-off-by: jld3103 <jld3103yt@gmail.com>

developer_manual/core/index.rst

@@ -9,6 +9,7 @@ Please make sure you have set up a :ref:`devenv`.
 .. toctree::
    :maxdepth: 2
 
+   static-analysis
    unit-testing
    externalapi
    architecture/index

developer_manual/core/static-analysis.rst

@@ -0,0 +1,31 @@
+===============
+Static analysis
+===============
+
+PHP static analysis
+-------------------
+
+In the server repository psalm is used for static analysis of the PHP code.
+
+Required PHP extensions
+^^^^^^^^^^^^^^^^^^^^^^^
+
+The following PHP extensions are required to be installed and enabled to make psalm work:
+
+* acpu
+* curl
+* ftp
+* gd
+* iconv
+* json
+* ldap
+* libxml
+* mbstring
+* openssl
+* pdo
+* simplexml
+* sysvsem
+* xmlreader
+* zip
+
+Some of these are for optional features, but are still required to validate the code.