DOCUMENTATION: Moved installation instructions to separate page (#561)

* DOCUMENTATION: Moved installation instructions to separate page

* Added Fedora to contents table
* Added Issue/Bug Report section to README
* Some minor improvements

* DOCUMENTATION: Rename directory doc to docs

* Also move ISSUE_TEMPLATE.md to docs directory

* DOCUMENTATION: Use current repo's files

* This makes it consistent instead  of having few local and few pointing to
  espressif/arduino-esp32 by all linking to local files

* DOCUMENTATION: Fix hyperlink to issue/bug template in contents

* DOCUMENTATION: contents: supress platform specific installation instruction

docs/esp-idf_component.md

@@ -0,0 +1,55 @@
+To use as a component of ESP-IDF
+=================================================
+
+- Download and install [esp-idf](https://github.com/espressif/esp-idf)
+- Create blank idf project (from one of the examples)
+- in the project folder, create a folder called components and clone this repository inside
+
+    ```bash
+    mkdir -p components && \
+    cd components && \
+    git clone https://github.com/espressif/arduino-esp32.git arduino && \
+    cd .. && \
+    make menuconfig
+  ```
+- ```make menuconfig``` has some Arduino options
+    - "Autostart Arduino setup and loop on boot"
+        - If you enable this options, your main.cpp should be formated like any other sketch
+
+          ```arduino
+          //file: main.cpp
+          #include "Arduino.h"
+
+          void setup(){
+            Serial.begin(115200);
+          }
+
+          void loop(){
+            Serial.println("loop");
+            delay(1000);
+          }
+          ```
+
+        - Else you need to implement ```app_main()``` and call ```initArduino();``` in it.
+
+          Keep in mind that setup() and loop() will not be called in this case.
+          If you plan to base your code on examples provided in [esp-idf](https://github.com/espressif/esp-idf/tree/master/examples), please make sure move the app_main() function in main.cpp from the files in the example.
+
+          ```arduino
+          //file: main.cpp
+          #include "Arduino.h"
+
+          extern "C" void app_main()
+          {
+              initArduino();
+              pinMode(4, OUTPUT);
+              digitalWrite(4, HIGH);
+              //do your own thing
+          }
+          ```
+    - "Disable mutex locks for HAL"
+        - If enabled, there will be no protection on the drivers from concurently accessing them from another thread/interrupt/core
+    - "Autoconnect WiFi on boot"
+        - If enabled, WiFi will start with the last known configuration
+        - Else it will wait for WiFi.begin
+- ```make flash monitor``` will build, upload and open serial monitor to your board