Converts README to markdown (no textual changes) for better display on #676

Job	Run time
Empty APLOGNO() test	30s
Default	3m 22s
All-static modules	3m 36s
Prefork MPM, all-modules (except cgid)	3m 58s
Worker MPM, all-modules	3m 51s
Shared MPMs, all-modules	3m 59s
Event MPM, all-modules, mod_cgid only	3m 48s
Event MPM, all-modules, no CMSG_DATA	4m 1s
Default, all-modules + install	4m 9s
Default, all-modules, random test order	3m 50s
GCC 10 maintainer-mode w/-Werror, install + VPATH	3m 16s
All-modules, APR 1.7.4, APR-util 1.6.3	5m 32s
APR 1.8.x, APR-util 1.7.x	5m 49s
Pool-debug	6m 0s
Shared MPMs (event), pool-debug, SSL/TLS variants	8m 59s
Shared MPMs (worker), pool-debug, SSL/TLS variants	8m 47s
Shared MPMs (prefork), pool-debug, SSL/TLS variants	8m 50s
litmus WebDAV tests	2m 16s
litmus WebDAV tests, APR trunk, LMDB	2m 12s
Regenerate ap_expr	3m 46s
APR 1.7.4, APR-util 1.6.3, LDAP	5m 38s
APR trunk thread debugging	4m 35s
UBSan	4m 41s
ASan	6m 15s
ASan, pool-debug	6m 58s
HTTP/2 test suite	12m 20s
MOD_TLS test suite	5m 2s
	2h 16m 0s

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