doc: add note on process.title max length

Fixes #5006.

doc/api/process.markdown

@@ -379,10 +379,21 @@ The PID of the process.
 
     console.log('This process is pid ' + process.pid);
 
+
 ## process.title
 
 Getter/setter to set what is displayed in 'ps'.
 
+When used as a setter, the maximum length is platform-specific and probably
+short.
+
+On Linux and OS X, it's limited to the size of the binary name plus the
+length of the command line arguments because it overwrites the argv memory.
+
+v0.8 allowed for longer process title strings by also overwriting the environ
+memory but that was potentially insecure/confusing in some (rather obscure)
+cases.
+
 
 ## process.arch