Fix some grammatical errors, typos, broken links in the TCMalloc design.
Fix some grammatical errors, typos, broken links in the TCMalloc design.

PiperOrigin-RevId: 408746803
Change-Id: I4958bc19159e9fb953c26a97c1005496c89184d6

google/tcmalloc,google/tcmalloc,google/tcmalloc