how do I apply a patch to a file?

[d3e608 at pnli.pnl.gov]

The title says it all.  I have a source file and a diff (?) file, and the
instructions say "apply the patch to the source file".  *How* ?  If this is
an RTFM, please excuse; I haven't a FM.  Thanks in advance.

Jeff Nye                   jp_nye at pnl.gov
Battelle PNL K6-10         voice:  (509) 376-4571, days, PDT 
PO Box 999                 Richland, WA 99352  

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