add some docs to the nix store which may help someone with the same problems

src/NixStore.zig

@@ -4,6 +4,10 @@ const std = @import("std");
 
 const gpa = std.heap.page_allocator;
 
+/// Add a path to the store, this will copy the contents of path recursively
+/// into the store and return a (hopefully) valid store path. To try and keep
+/// this store path valid you should follow this with a call to realize() and
+/// then root the store path.
 pub fn add(path: []const u8) error{Failure}![]const u8 {
     const res = std.process.Child.run(.{
         .allocator = gpa,
@@ -13,6 +17,9 @@ pub fn add(path: []const u8) error{Failure}![]const u8 {
     return res.stdout[0 .. res.stdout.len - 1]; // to chop off the \n
 }
 
+/// This tries to tell the store that a store_path should stick around a while
+/// longer, there's a chance that it doesn't listen and removes that store_path
+/// but in my testing it seemed to stick around.
 pub fn realize(store_path: []const u8) error{Failure}!void {
     _ = std.process.Child.run(.{
         .allocator = gpa,
@@ -21,6 +28,9 @@ pub fn realize(store_path: []const u8) error{Failure}!void {
     return;
 }
 
+/// This tells the nix store to not gc our new store_path because it has a
+/// dependency at root_path and that only if root_path doesn't exist anymore
+/// it can delete store_path.
 pub fn root(store_path: []const u8, root_path: []const u8) error{Failure}!void {
     _ = std.process.Child.run(.{
         .allocator = gpa,
@@ -29,6 +39,7 @@ pub fn root(store_path: []const u8, root_path: []const u8) error{Failure}!void {
     return;
 }
 
+/// Delete a path from the store.
 pub fn delete(store_path: []const u8) error{Failure}!void {
     _ = std.process.Child.run(.{
         .allocator = gpa,