I think either is acceptable if both are in the same document and thus presumably published at the same time. The present tense is from the point of view that the entire document is there, available to read. The future tense is from the point of view that the reader is progressing through the sections in order and hasn't gotten to later sections yet.
For a reference book which is not intended to be read cover to cover, but rather in which the reader will refer to sections as the need arises, I'd make all references present tense.
So you can use either, but be consistent. Also be consistent between forward and backward references. That is, don't make references to later chapters in the future tense but references to previous chapters in the present tense. Either make them all present tense, or make forward references future and backward references past.
If you are referring to something not yet published, use the future. Like, "This will be discussed in the next issue of our newsletter."