scripts/spelling.txt: add "an user" pattern and fix typo instances

Fix typos and add the following to the scripts/spelling.txt:

  an user||a user
  an userspace||a userspace

I also added "userspace" to the list since it is a common word in Linux.
I found some instances for "an userfaultfd", but I did not add it to the
list.  I felt it is endless to find words that start with "user" such as
"userland" etc., so must draw a line somewhere.

Link: http://lkml.kernel.org/r/1481573103-11329-4-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/tools/perf/Documentation/tips.txt b/tools/perf/Documentation/tips.txt
index 8a6479c..170b028 100644
--- a/tools/perf/Documentation/tips.txt
+++ b/tools/perf/Documentation/tips.txt
@@ -22,7 +22,7 @@
 For memory address profiling, try: perf mem record / perf mem report
 For tracepoint events, try: perf report -s trace_fields
 To record callchains for each sample: perf record -g
-To record every process run by an user: perf record -u <user>
+To record every process run by a user: perf record -u <user>
 Skip collecing build-id when recording: perf record -B
 To change sampling frequency to 100 Hz: perf record -F 100
 See assembly instructions with percentage: perf annotate <symbol>