Add readme.md for 'tools' directory

tools/readme.md

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+## Cppcheck developer and build tools
+
+### * tools/matchcompiler.py
+
+The matchcompiler.py is a build script that performs a few code transformations to *.cpp* files under the *lib* directory. These transformations are related to the use of `Token::Match()` function and are intented to improve code performance. The transformed files are saved on the *build* directory. This tool is silently used when building the code with `SRCDIR=build`, that is:
+```shell
+$ cd path/to/cppcheck
+$ make SRCDIR=build
+```
+Here is a simple example of the *matchcompiler.py* optimization. Suppose there is a file *example.cpp* under *lib/*:
+```cpp
+// lib/example.cpp
+void f1() {
+    Token::Match(tok, "abc");
+}
+
+void f2() {
+    const char *abc = "abc";
+    Token::Match(tok, abc);
+}
+```
+If you manually run *matchcompiler.py* from the main directory:
+```shell
+$ cd path/to/cppcheck
+$ python tools/matchcompiler.py
+```
+A file *example.cpp* will be generated on the *build* directory:
+```cpp
+// build/example.cpp
+#include "token.h"
+#include "errorlogger.h"
+#include <string>
+#include <cstring>
+static const std::string matchStr1("abc");
+// pattern: abc
+static bool match1(const Token* tok) {
+    if (!tok || !(tok->str()==matchStr1)/* abc */)
+        return false;
+    return true;
+}
+void f1() {
+    match1(tok);
+}
+
+void f2() {
+    const char *abc = "abc";
+    Token::Match(tok, abc);
+}
+```
+From this we can see that the usage of `Token::Match()` in `f1()` has been optimized, whereas the one in `f2()` couldn't be optimized (the string wasn't inline on the `Token::Match()` call). **The developer doesn't need to use this tool during development but should be aware of these optimizations**. *Building with this optimization, cppcheck can get a boost of 2x of speed-up.* 
+
+### * tools/dmake.cpp
+
+Automatically generates the main `Makefile` for Cppcheck (**the main `Makefile` should not be modified manually**). To build and run the `dmake` tool execute:
+```shell
+$ cd path/to/cppcheck
+$ make dmake
+$ ./dmake
+```
+### * tools/reduce.cpp
+
+Cppcheck tool that reduces code for a hang/false positive. To build the tool run:
+```shell
+$ cd path/to/cppcheck
+$ make reduce
+```
+
+### * tools/times.sh
+
+Script to generate a `times.log` file that contains timing information of the last 20 revisions.
+