Update JobKeywords.md file

Signed-off-by: Vitalii Koshura <lestat.de.lionkur@gmail.com>

JobKeywords.md

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+# Job keywords
+
+[Keywords](DesignKeywords) describe the attributes of jobs, such as:
+* The area of science it contributes to
+* The location of the research group that submitted it.
+
+Keywords are used for various purposes in BOINC, such as
+* Informational: volunteers can see job keywords in the BOINC Manager
+   and on the project web site.
+* Preferences: volunteers can express preferences for keywords,
+   which limits what jobs are sent to the volunteer.
+   Currently this is supported in the account manager architecture;
+   it would also be possible to support it at the project level.
+
+The set of keywords is decided by the community.
+If you want a keyword that's not there, please contact David Anderson.
+
+## Keyword headers
+
+Keywords are identified by permanent integer IDs, and also by symbols mapped to these IDs.
+The current list of keywords can be obtained as:
+
+* [an XML file](https://boinc.berkeley.edu/keywords.php)
+* [a web page](https://boinc.berkeley.edu/keywords.php?header=html)
+* [a Python header file](https://boinc.berkeley.edu/keywords.php?header=python)
+* [a C header file](https://boinc.berkeley.edu/keywords.php?header=c)
+* [a Bash header file ](https://boinc.berkeley.edu/keywords.php?header=bash)
+* [a PHP header file ](https://boinc.berkeley.edu/keywords.php?header=php)
+
+## Keywords in job submission
+
+The [job submission interfaces](JobSubmission) let you associate keywords with jobs.
+
+## Keyword scheduling
+
+If you include
+```
+<keyword_sched/>
+```
+in your project's config.xml, score-based scheduling will include a keyword component:
+if a volunteer has a "no" preference for keyword X,
+they won't be sent jobs with keyword X,
+and if they have a "yes" preference,
+they will preferentially be sent jobs with that keyword.
+
+## Project keywords
+
+You can also associate keywords with your project as a whole.
+Do this by creating a file "project_keywords.xml" in the project root directory.
+This file has the format
+```
+<project_keywords>
+   <keyword>
+      <id>4</id>
+      { <work_fraction>.7</work_fraction> }
+   </keyword>
+   ...
+</project_keywords>
+```
+
+Include \<work_fraction> if not all jobs have that keyword.
+The number express what fraction of your project's work (measured in FLOPs)
+have that keyword.
+
+The information in this file is exported in your project's get_project_config.php.
+It's not currently used for anything.
+It will be used for various project-browsing purposes in the future.