cmd/pprof: update README to explain relationship with github.com/google/pprof
cmd/pprof: update README to explain relationship with github.com/google/pprof

For google/pprof#132.

Change-Id: I73785bc8662565ff7b2fac66e23497dd06fc25b6
Reviewed-on: https://go-review.googlesource.com/40231
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

nawawi/go,polyverse-security/go,cloudflare/go,nawawi/go,ImJasonH/go,ImJasonH/go,akutz/go,Cofyc/go,golang/go,codestation/go,ImJasonH/go,josharian/go,polyverse-security/go,polyverse-security/go,akutz/go,ImJasonH/go,nawawi/go,vsekhar/elastic-go,akutz/go,polyverse-security/go,ImJasonH/go,codestation/go,ImJasonH/go,cloudflare/go,codestation/go,akutz/go,cloudflare/go,josharian/go,golang/go,nawawi/go,polyverse-security/go,cloudflare/go,nawawi/go,vsekhar/elastic-go,CAFxX/go,akutz/go,nawawi/go,CAFxX/go,vsekhar/elastic-go,Cofyc/go,derekmarcotte/go,derekmarcotte/go,golang/go,christopher-henderson/Go,derekmarcotte/go,ImJasonH/go,derekmarcotte/go,codestation/go,derekmarcotte/go,CAFxX/go,CAFxX/go,codestation/go,cloudflare/go,polyverse-security/go,josharian/go,josharian/go,akutz/go,vsekhar/elastic-go,vsekhar/elastic-go,derekmarcotte/go,polyverse-security/go,derekmarcotte/go,josharian/go,vsekhar/elastic-go,CAFxX/go,nawawi/go,codestation/go,nawawi/go,golang/go,polyverse-security/go,josharian/go,golang/go,CAFxX/go,Cofyc/go,cloudflare/go,akutz/go,ImJasonH/go,CAFxX/go,Cofyc/go,cloudflare/go,vsekhar/elastic-go,golang/go,Cofyc/go,Cofyc/go,CAFxX/go,codestation/go,golang/go,derekmarcotte/go,codestation/go,Cofyc/go,cloudflare/go,vsekhar/elastic-go,akutz/go,golang/go,josharian/go,josharian/go,Cofyc/go