Actually add HowToReview.txt

doc/HACKING/HowToReview.txt

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+How to review a patch
+=====================
+
+Some folks have said that they'd like to review patches more often, but they
+don't know how.
+
+So, here are a bunch of things to check for when reviewing a patch!
+
+Note that if you can't do every one of these, that doesn't mean you can't do
+a good review!  Just make it clear what you checked for and what you didn't.
+
+
+Top-level smell-checks
+----------------------
+
+(Difficulty: easy)
+
+Does it compile with --enable-gcc-warnings?
+
+Does 'make check-spaces' pass?
+
+Does it have a reasonable amount of tests?  Do they pass?  Do they leak
+memory?
+
+Do all the new functions, global variables, types, and structure members have
+documentation?
+
+Do all the the functions, global variables, types, and structure members with
+modified behavior have modified documentation?
+
+Do all the new torrc options have documentation?
+
+If this changes Tor's behavior on the wire, is there a design proposal?
+
+
+
+Let's look at the code!
+-----------------------
+
+Does the code conform to CodingStandards.txt?
+
+Does the code leak memory?
+
+If two or more pointers ever point to the same object, is it clear which
+pointer "owns" the object?
+
+Are all allocated resources freed?
+
+Are all pointers that should be const, const?
+
+Are #defines used for 'magic' numbers?
+
+Can you understand what the code is trying to do?
+
+Can you convince yourself that the code really does that?
+
+Is there duplicated code that could be turned into a function?
+
+
+Let's look at the documentation!
+--------------------------------
+
+Does the documentation confirm to CodingStandards.txt?
+
+Does it make sense?
+
+Can you predict what the function will do from its documentation?
+
+
+Let's think about security!
+---------------------------
+
+If there are any arrays, buffers, are you 100% sure that they cannot
+overflow?
+
+If there is any integer math, can it overflow or underflow?
+
+If there are any allocations, are you sure there are corresponding
+deallocations?
+
+Is there a safer pattern that could be used in any case?
+
+Have they used one of the Forbidden Functions?
+
+(Also see your favorite secure C programming guides.)