docs: convert to .rst and add readthedocs

doc/esp8266wifi/client-secure-class.rst

@@ -0,0 +1,78 @@
+:orphan:
+
+Client Secure Class
+-------------------
+
+Methods and properties described in this section are specific to ESP8266. They are not covered in `Arduino WiFi library <https://www.arduino.cc/en/Reference/WiFi>`__ documentation. Before they are fully documented please refer to information below.
+
+loadCertificate
+~~~~~~~~~~~~~~~
+
+Load client certificate from file system.
+
+.. code:: cpp
+
+    loadCertificate(file) 
+
+*Declarations*
+
+.. code:: cpp
+
+    #include <FS.h>
+    #include <ESP8266WiFi.h>
+    #include <WiFiClientSecure.h>
+
+    const char* certyficateFile = "/client.cer";
+
+*setup() or loop()*
+
+.. code:: cpp
+
+    if (!SPIFFS.begin()) 
+    {
+      Serial.println("Failed to mount the file system");
+      return;
+    }
+
+    Serial.printf("Opening %s", certyficateFile);
+    File crtFile = SPIFFS.open(certyficateFile, "r");
+    if (!crtFile)
+    {
+      Serial.println(" Failed!");
+    }
+
+    WiFiClientSecure client;
+
+    Serial.print("Loading %s", certyficateFile);
+    if (!client.loadCertificate(crtFile))
+    {
+      Serial.println(" Failed!");
+    }
+
+    // proceed with connecting of client to the host
+
+setCertificate
+~~~~~~~~~~~~~~
+
+Load client certificate from C array.
+
+.. code:: cpp
+
+    setCertificate (array, size) 
+
+For a practical example please check `this interesting blog <https://nofurtherquestions.wordpress.com/2016/03/14/making-an-esp8266-web-accessible/>`__.
+
+Other Function Calls
+~~~~~~~~~~~~~~~~~~~~
+
+.. code:: cpp
+
+    bool  verify (const char *fingerprint, const char *domain_name) 
+    void  setPrivateKey (const uint8_t *pk, size_t size) 
+    bool  loadCertificate (Stream &stream, size_t size) 
+    bool  loadPrivateKey (Stream &stream, size_t size) 
+    template<typename TFile >  bool  loadPrivateKey (TFile &file)
+
+Documentation for the above functions is not yet prepared.
+
+For code samples please refer to separate section with `examples <client-secure-examples.md>`__ dedicated specifically to the Client Secure Class.