Update Etags wiki to reference current directories

[yfguo]

Summary

• update the Etags documentation to prune the current Hydra process manager directory
• point the PMI find command to the existing include and src directories

Testing

• find src ( ( -path src/mpid -o -path src/pm/hydra -o -path src/pmi -o -path src/mpi/romio -o -path src/binding -o -path src/mpe2 -o -path src/util/multichannel ) -prune -o -name '.[chi]' -o -name '.h.in' ) -a ! -name state_names.h -a ! -name mpiallstates.h -a ! -name defmsg.h -a ! -name windefmsg.h -a ! -name 'tokens.[ch]' -a ! -name 'parser.[ch]' -a ! -name '.#' -type f -print | wc -l
• find src/pmi/include src/pmi/src src/mpid/ch3/channels/nemesis src/mpid/common src/mpid/ch3 ( -path src/mpid/common/sock/iocp -o -path src/mpid/ch3/channels -o -path src/mpid/ch3/channels/nemesis/nemesis/netmod/wintcp ) -prune -o ( -name '.[chi]' -o -name '.h.in' ) -a ! -name '.#' -a ! -name 'tokens.[ch]' -a ! -name 'parser.[ch]' -print | wc -l

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https://chatgpt.com/codex/tasks/task_e_68d7518de0988325aff1f90ca273f85e