[exponent-docs] Add camera permission type on permissions.rst
[exponent-docs] Add camera permission type on permissions.rst

Document Exponent.Permissions.CAMERA

Closes #10

exponent/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponentjs/exponent