Flash Builder uses ASDocs, which are embedded inside the SWC, to provide code hints - unfortunately, FB doesnt include the docs when it builds a SWC.
However, it can be done 'manually' with ANT:
<target name="insertASDocs">
<zip destfile="PATH_TO_YOUR_SWC" update="true">
<zipfileset dir="ASDOCS_FOLDER/tempdita" prefix="docs">
<include name="*.*"/>
<exclude name="ASDoc_Config.xml"/>
<exclude name="overviews.xml"/>
</zipfileset>
</zip>
</target>
PATH_TO_YOUR_SWC is the relative path and swc name (eg: myFolder/mySwc.swc). ASDOCS_FOLDER is the folder where your generated docs are stored.
The ANT script just adds the ASDocs to the SWC - after this, code hints should appear.
Update:
Forgot to mention that you need to set keep-xml to true when generating the docs (if inserting them into a swc):
<asdoc keep-xml="true" ...