Remove `man` from `.gitignore`

Changes to be committed:
modified:   .gitignore
new file:   man/classr.Rd
new file:   man/createInstance-character-ANY-method.Rd
new file:   man/createInstance-character-missing-method.Rd
new file:   man/createInstance.Rd
new file:   man/ensureClassRegistration-character-method.Rd
new file:   man/ensureClassRegistration.Rd