netresolv: Add a quick document on how to synchronize with NetBSD.

src/kits/network/netresolv/HowTo-Synchronize_with_NetBSD.md

@@ -0,0 +1,30 @@
+How to Merge Patches from NetBSD Trunk
+============================================
+Using the NetBSD CVS is a pain, so instead, the preferred thing to do is to use
+[IIJ's Git mirror](https://github.com/IIJ-NetBSD/netbsd-src). The code here is
+in the tree at a few places:`inet` is at `lib/libc/inet`, irs is scattered
+across the tree, and `resolv` is at `lib/libc/resolv`.
+
+The preferable way to merge is to take the last commit merged from IIJ's mirror
+(can be found in the merging commit in Haiku, if the merger has done their work
+properly) and check all commits since then to see if they apply or not (some
+apply to documentation we don't have, etc.) Cherry-pick the ones that do, and
+download them as git-format-patch patches (by adding `.patch` onto the end of the
+commit URL).
+
+To convert the patches to have the correct paths to the resolv/inet/etc. code, use
+`sed`:
+```
+sed s%lib/libc/resolv%src/kits/network/netresolv/resolv%g -i *.patch
+```
+(You'll need to use similar commands for the `inet` and `irs` code.)
+
+Then apply the patches using `git apply --reject file.patch`. Git will spew a lot of
+errors about files in the patch that aren't in the tree, and then it will warn that
+some hunks are being rejected. Review the rejected hunks **VERY CAREFULLY**, as
+some code in Haiku's NetResolv is not in NetBSD's and vice versa, and so some patches
+may not apply cleanly because of that. You might have to resort to merging those
+hunks by hand, if they apply at all to Haiku's code.
+
+Commit the changes all at once, but list all the commits merged from NetBSD
+in the commit message (see previous merges for the style to follow).