[enh] Add documentation on user/profile index

doc/API.md

@@ -103,6 +103,57 @@ For example, a deletion on `message/inbox` should send this document:
 
 #### `user/profile`
 
+
+ - Get an profile, by public key: `user/profile/<pubkey>`
+ - Add a new profile: `user/profile` (POST)
+ - Update an existing profile: `user/profile/_update` (POST)
+ - Delete an existing invitation: `invitation/certification/_delete` (POST)
+ - Search on profiles: `user/profile/_search` (POST or GET)
+
+A profile document is a JSON document. Mandatory fields are:
+ 
+ - `title`: user name (Lastanem, firstname...)
+ - `time`: submission time, in seconds
+ - `issuer`: user public key
+ - `hash`: hash of the JSON document (without fields `hash` and `signature`)
+ - `signature`: signature of the JSON document (without fields `hash` and `signature`)
+
+Example with only mandatory fields:
+
+```json
+{
+    "title" : "Pecquot Ludovic",
+    "description" : "Développeur Java et techno client-serveur\nParticipation aux #RML7, #EIS et #Sou",
+    "time" : 1488359903,
+    "issuer" : "2v6tXNxGC1BWaJtUFyPJ1wJ8rbz9v1ZVU1E1LEV2v4ss",
+    "hash" : "F66D43ECD4D38785F424ADB68B3EA13DD56DABDE275BBE780E81E8D4E1D0C5FA",
+    "signature" : "3CWxdLtyY8dky97RZBFLfP6axnfW8KUmhlkiaXC7BN98yg6xE9CkijRBGmuyrx3llPx5HeoGLG99DyvVIKZuCg=="
+}
+```
+
+Some additional fields are `description`, `socials`, `tags` and `avatar` :
+
+```json
+{
+    "title" : "Cédric Moreau",
+    "description" : "#Duniter developer",
+    "city" : "Rennes",
+    "socials" : [ {
+      "type" : "diaspora",
+      "url" : "https://diaspora-fr.org/people/f9d13420f9ff013197aa01beea1f31e2"
+    } ],
+    "time" : 1487422234,
+    "tags" : [ "Duniter" ],
+    "issuer" : "2ny7YAdmzReQxAayyJZsyVYwYhVyax2thKcGknmQy5nQ",
+    "avatar" : {
+      "_content_type" : "image/png",
+      "_content" : "iVBORw0KGgoAAAANSUhEUgAAAGQAAABkC(...)" // base 64 encoding
+    }
+    "hash" : "85F527077D060E03ECAC6D1AE38A74CCC900ACAF5D52F194BA34F5A5E8A55139",
+    "signature" : "WeP7JEwttAoSkHcuiFwo6N4SM0uVakTYBQ09H1+K8/nPFyxO3ak1U9EQ6qaQFoAx9IdDp5qO2EX662wP/pcEAg==",
+}
+```
+
 #### `user/settings`
 
 ### `message/*`