some rules for contribution added

Contributing.md

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+# Contributing to StreamDevice
+
+Contributions from the EPICS community (and others) are welcome.
+To ease the integration process, please follow the following guidelines.
+
+All contributions should be done as a pull request to the git repository
+https://github.com/paulscherrerinstitute/StreamDevice. Make sure to provide
+meaningful commit messages (no essay but more than "changes").
+
+For small modifications, a patch file is sufficient. Send it to me or better
+create an issue on https://github.com/paulscherrerinstitute/StreamDevice/issues
+and attach the patch file.
+
+Justify your change requests. Write a short summary for your pull request
+to explain what the change is about and what it improves or which bug it
+fixes. Use the issue system on github to report bugs.
+
+I reserve the right to accept or reject contributions or to request
+modifications before I accept them.
+
+Of course, you may as well report bugs without providing a solution yourself.
+
+## Code compatibility
+
+All code must compile for any EPICS release from at least R3.14.12 up to the
+latest one. Likewise the code must be compatible with any operating system
+supported by EPICS, like Linux, Windows, MacOS, RTEMS and VxWorks.
+In particular VxWorks 5 compatibility rules out many modern C++ features.
+But there are also other platforms that for example do not support C++11, so
+don't use it. 
+There should also be no compiler warning on any OS.
+
+Avoid compiler dependent features like #pragmas, assumptions on byte order,
+type size (in particular the size of pointers and long int) and other
+non-portable things like the availability of certain header files. Make sure
+non-portable code parts are enclosed in proper compiler branches and provide
+working implementations for all architectures.
+
+Make sure that the code in AsynDriverInterface stays compatible with old
+and new versions of asyn driver.
+
+The core of StreamDevice does not depend on EPICS. This is on purpose, to be
+able to use it in other control system frameworks. Modifications should not
+add EPICS dependencies except to StreamEpics and AsynDriverInterface, or the
+new dependency must be in a separate file which can be left out of the build
+without jeopardizing the main functionality of StreamDevice.
+
+The code must not depend on external libraries that may not be available on
+all systems, except if provided as a separate file which can be left out of
+the build on platforms that do not support the library.
+
+## Language
+
+Write in English. That includes all identifiers (variables, functions, ...),
+comments, documentation and commit messages. Check your spelling.
+
+## File formats
+
+All files are in Unix format (\n line terminators). Do not change them to
+any other format (e.g. Windows with \r\n terminators). Do not add new files in
+other formats.
+
+The files must contain only ASCII characters. Do not use any Unicode multi-byte
+characters (including byte order marks) or any pre-Unicode code page dependent
+characters (e.g. umlaut), not even in comments. Do not use form feed, vertical
+tab, or other control characters except newline.
+
+Indents are 4 spaces. Do not use tabs (except in Makefiles). Make sure your
+editor is set up accordingly.
+
+Files must end in a newline and there must be no spaces at the end of lines.
+Do not add excessive amount of newlines at the end of files.
+
+Do not add any editor configurations (e.g. for emacs) to the files. Also do
+not add any configuration files or directories for development environments,
+editors, etc.
+
+-------
+
+Dirk Zimoch <dirk.zimoch@psi.ch>, June 2021
+