add dev doc

DEVELOPING.md

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+# Being a Hush Developer
+
+## Compiling Hush
+
+Normal compiling is as simple as:
+
+	./zcutil/build.sh
+
+To make it use as many CPU threads as you have:
+
+	./zcutil/build.sh -j$(nproc)  # assumes linux
+	./zcutil/build.sh -j8 		  # use a fixed 8 threads, more portable
+
+## Good Hygiene
+
+To avoid weirld build system issues, it's often good to run:
+
+	make clean
+
+*before* you switch Git branches. Otherwise, the new branches Makefiles
+often are incompatible and `make clean` will be impossible, which can
+sometimes introduce weird bugs or make compiling really annoying.
+
+## Switching branches
+
+Switching branches and doing partial compiles in Komodo/Hush source code
+can introduce weird bugs, which are fixed by running `build.sh` again.
+When in doubt, if you run into a compile error, especially if it mentions
+`OCTET_STRING`, run `build.sh` again. Running `make clean` before switching
+branches can often prevent those problems.
+
+## Partial compiles
+
+At any point, you can modify hush source code and then use `make` or `build.sh`
+to do a partial compile. The first is faster but the latter is more likely to
+work correctly in all circustances. Sometimes partial compiles break weird
+build system dependencies, and you must do a `make clean` first, or even
+`git clean -fdx` (look up what it means first!) to clean things. The nuclear
+option is to re-clone the repo, which sometimes is the least work to fix
+the problem.
+
+## Generating new unix man pages
+
+Make sure that you have updated all version numbers in hushd and compiled, then
+to generate new unix man pages for that version :
+
+	./contrib/devtools/gen-manpages.sh
+
+## Generating new debian packages
+
+After successfully compiling Hush, you can generate a debian package of these binaries with:
+
+	./zcutil/build-debian-package.sh
+
+This command will not work on Mac OS X. Currently  you cannot generate a Debian package
+from operating systems other than Linux.
+