add http example

[mazrean]

I created an example application using httpform.

[github-actions]

Benchmark Result

goos: linux
goarch: amd64
pkg: github.com/mazrean/formstream
cpu: AMD EPYC 7763 64-Core Processor                
BenchmarkFormStreamFastPath/1MB-4 	    2912	    412447 ns/op	   10023 B/op	      64 allocs/op
BenchmarkFormStreamFastPath/10MB-4         	     290	   4096840 ns/op	   10032 B/op	      64 allocs/op
BenchmarkFormStreamFastPath/100MB-4        	      27	  42262177 ns/op	   10315 B/op	      64 allocs/op
BenchmarkFormStreamFastPath/1GB-4          	       3	 431718730 ns/op	   12906 B/op	      65 allocs/op
BenchmarkFormStreamSlowPath/1MB-4          	    2475	    447454 ns/op	   15222 B/op	      69 allocs/op
BenchmarkFormStreamSlowPath/10MB-4         	     242	   4942772 ns/op	  148805 B/op	      69 allocs/op
BenchmarkFormStreamSlowPath/100MB-4        	       5	 228078568 ns/op	26890019 B/op	      80 allocs/op
BenchmarkFormStreamSlowPath/1GB-4          	       1	2325371343 ns/op	134269624 B/op	     100 allocs/op
BenchmarkStdMultipartReadForm/1MB-4        	    1310	    839953 ns/op	 4203629 B/op	      61 allocs/op
BenchmarkStdMultipartReadForm/10MB-4       	     129	   8808210 ns/op	33566528 B/op	      64 allocs/op
BenchmarkStdMultipartReadForm/100MB-4      	       5	 243942854 ns/op	134263774 B/op	      74 allocs/op
BenchmarkStdMultipartReadForm/1GB-4        	       1	2520541646 ns/op	134267176 B/op	      76 allocs/op
PASS
ok  	github.com/mazrean/formstream	24.889s

pprof command

gh api /repos/mazrean/formstream/actions/artifacts/1306158860/zip > /tmp/profile.zip
unzip /tmp/profile.zip -d profile
rm -rf /tmp/profile.zip
go tool pprof -http :6060 profile/cpu.out