Adding requirements.txt into MANIFEST.in #397

Job	Run time
Docs	1m 58s
CI (macos-15-intel, pypy-3.10)	1m 44s
CI (macos-15-intel, 3.9)	26s
CI (macos-latest, 3.10)	2m 24s
CI (macos-latest, pypy-3.10)	47s
CI (macos-15-intel, 3.11)	31s
CI (macos-15-intel, 3.10)	27s
CI (macos-latest, 3.9)	3m 25s
CI (windows-latest, 3.10)	46s
CI (macos-latest, 3.11)	21s
CI (windows-latest, 3.9)	1m 2s
CI (macos-latest, pypy-3.8)	54s
Integration (ubuntu-latest, 3.11)	44s
Integration (macos-15-intel, pypy-3.8)	1m 42s
Integration (macos-15-intel, 3.10)	43s
CI (macos-15-intel, pypy-3.8)	1m 21s
Integration (ubuntu-latest, pypy-3.8)	52s
Integration (windows-latest, pypy-3.10)	2m 7s
Integration (windows-latest, 3.9)	1m 14s
Integration (macos-latest, 3.10)	53s
CI (ubuntu-latest, pypy-3.8)	56s
CI (ubuntu-latest, 3.10)	19s
CI (ubuntu-latest, 3.11)	24s
Integration (ubuntu-latest, pypy-3.10)	1m 6s
Integration (ubuntu-latest, 3.10)	39s
Integration (windows-latest, 3.10)	1m 8s
Integration (ubuntu-latest, 3.9)	33s
CI (windows-latest, pypy-3.8)	2m 41s
CI (windows-latest, 3.11)	1m 2s
Integration (macos-15-intel, pypy-3.10)	1m 26s
Integration (macos-latest, pypy-3.10)	1m 9s
Integration (macos-15-intel, 3.9)	1m 6s
CI (windows-latest, pypy-3.10)	1m 52s
Integration (macos-latest, pypy-3.8)	49s
Integration (macos-latest, 3.9)	1m 1s
CI (ubuntu-latest, pypy-3.10)	1m 6s
CI (ubuntu-latest, 3.9)	22s
Integration (windows-latest, 3.11)	1m 20s
Integration (windows-latest, pypy-3.8)	11s
Integration (macos-15-intel, 3.11)	43s
Integration (macos-latest, 3.11)	45s
	44m 59s

Provide feedback